[RISCV][MC] Remove tautological CHECK-UNKNOWN disassembly checks (NFC) (#193682)

Many RISC-V MC tests assemble with `--mattr=+v` (or another extension),
then run llvm-objdump on the result *without* `--mattr=`, expecting the
disassembler to print `<unknown>` for every instruction. These
CHECK-UNKNOWN lines only restate the encoded bytes that are already
verified by CHECK-ENCODING from `llvm-mc -show-encoding`, so they do not
add coverage.

Drop the CHECK-UNKNOWN RUN lines and check directives from the affected
tests to reduce noise and make the tests easier to read. The remaining
CHECK-INST / CHECK-ENCODING / CHECK-ERROR coverage is unchanged.

This is a preparatory cleanup that makes the upcoming llvm-objdump
per-region disassembly change (using ISA mapping symbols #193448) easier
to review.

Assisted-by: Claude Opus
I use Opus to write commit message...:P

Author: kito-cheng

llvm/test/MC/RISCV/XTHeadVdot-valid.s

@@ -5,89 +5,73 @@
 # RUN: llvm-mc -triple=riscv64 -filetype=obj --mattr=+xtheadvdot %s \
 # RUN:        | llvm-objdump -d --mattr=+xtheadvdot - \
 # RUN:        | FileCheck %s --check-prefix=CHECK-INST
-# RUN: llvm-mc -triple=riscv64 -filetype=obj --mattr=+xtheadvdot %s \
-# RUN:        | llvm-objdump -d - | FileCheck %s --check-prefix=CHECK-UNKNOWN
 
 th.vmaqau.vv v8, v20, v4, v0.t
 # CHECK-INST: th.vmaqau.vv v8, v20, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x88]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 884a640b <unknown>
 
 th.vmaqau.vv v8, v20, v4
 # CHECK-INST: th.vmaqau.vv v8, v20, v4
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x8a]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 8a4a640b <unknown>
 
 th.vmaqau.vx v8, a0, v4, v0.t
 # CHECK-INST: th.vmaqau.vx v8, a0, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x8c]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 8c45640b <unknown>
 
 th.vmaqau.vx v8, a0, v4
 # CHECK-INST: th.vmaqau.vx v8, a0, v4
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x8e]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 8e45640b <unknown>
 
 th.vmaqa.vv v8, v20, v4, v0.t
 # CHECK-INST: th.vmaqa.vv v8, v20, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x80]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 804a640b <unknown>
 
 th.vmaqa.vv v8, v20, v4
 # CHECK-INST: th.vmaqa.vv v8, v20, v4
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x82]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 824a640b <unknown>
 
 th.vmaqa.vx v8, a0, v4, v0.t
 # CHECK-INST: th.vmaqa.vx v8, a0, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x84]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 8445640b <unknown>
 
 th.vmaqa.vx v8, a0, v4
 # CHECK-INST: th.vmaqa.vx v8, a0, v4
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x86]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 8645640b <unknown>
 
 th.vmaqasu.vv v8, v20, v4, v0.t
 # CHECK-INST: th.vmaqasu.vv v8, v20, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x90]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 904a640b <unknown>
 
 th.vmaqasu.vv v8, v20, v4
 # CHECK-INST: th.vmaqasu.vv v8, v20, v4
 # CHECK-ENCODING: [0x0b,0x64,0x4a,0x92]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 924a640b <unknown>
 
 th.vmaqasu.vx v8, a0, v4, v0.t
 # CHECK-INST: th.vmaqasu.vx v8, a0, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x94]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 9445640b <unknown>
 
 th.vmaqasu.vx v8, a0, v4
 # CHECK-INST: th.vmaqasu.vx v8, a0, v4
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x96]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 9645640b <unknown>
 
 th.vmaqaus.vx v8, a0, v4, v0.t
 # CHECK-INST: th.vmaqaus.vx v8, a0, v4, v0.t
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x9c]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 9c45640b <unknown>
 
 th.vmaqaus.vx v8, a0, v4
 # CHECK-INST: th.vmaqaus.vx v8, a0, v4
 # CHECK-ENCODING: [0x0b,0x64,0x45,0x9e]
 # CHECK-ERROR: instruction requires the following: 'XTHeadVdot' (T-Head Vector Extensions for Dot){{$}}
-# CHECK-UNKNOWN: 9e45640b <unknown>