[llvm] ARM: Remove override of shouldRewriteCopySrc (PR #125219)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-debian` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/18417

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/ARM/shouldRewriteCopySrc.ll' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=arm-none-eabihf -mcpu=cortex-a55 < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/ARM/shouldRewriteCopySrc.ll | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/ARM/shouldRewriteCopySrc.ll # RUN: at line 2
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/ARM/shouldRewriteCopySrc.ll
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=arm-none-eabihf -mcpu=cortex-a55

# After Peephole Optimizations
# Machine code for function shouldRewriteCopySrc: IsSSA, TracksLiveness
Function Live Ins: $d0 in %0

bb.0.bb:
  liveins: $d0
  %0:dpr = COPY $d0
  %1:dpr = VADDD %0:dpr, %0:dpr, 14, $noreg
  INLINEASM &nop [sideeffect] [attdialect], $0:[clobber], implicit-def early-clobber $q0, $1:[clobber], implicit-def early-clobber $q1, $2:[clobber], implicit-def early-clobber $q2, $3:[clobber], implicit-def early-clobber $q3, $4:[clobber], implicit-def early-clobber $q4, $5:[clobber], implicit-def early-clobber $q5, $6:[clobber], implicit-def early-clobber $q6, $7:[clobber], implicit-def early-clobber $q7
  %2:gpr, %3:gpr = VMOVRRD %1:dpr, 14, $noreg
  %5:spr = COPY %1.ssub_0:dpr
  $s0 = COPY %5:spr
  BX_RET 14, $noreg, implicit $s0

# End machine code for function shouldRewriteCopySrc.

*** Bad machine code: Invalid register class for subregister index ***
- function:    shouldRewriteCopySrc
- basic block: %bb.0 bb (0x9947838)
- instruction: %5:spr = COPY %1.ssub_0:dpr
- operand 1:   %1.ssub_0:dpr
Register class DPR does not fully support subreg index ssub_0
LLVM ERROR: Found 1 machine code errors.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=arm-none-eabihf -mcpu=cortex-a55
1.	Running pass 'Function Pass Manager' on module '<stdin>'.
2.	Running pass 'Verify generated machine code' on function '@shouldRewriteCopySrc'
 #0 0x0000000003904db7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x3904db7)
 #1 0x000000000390286e llvm::sys::RunSignalHandlers() (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x390286e)
 #2 0x000000000390546a SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x00007fa85b978140 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x13140)
 #4 0x00007fa85b48cd61 raise (/lib/x86_64-linux-gnu/libc.so.6+0x38d61)
 #5 0x00007fa85b476537 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22537)
 #6 0x000000000386e8ca llvm::report_fatal_error(llvm::Twine const&, bool) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x386e8ca)
 #7 0x0000000002ae05fd (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2ae05fd)
 #8 0x0000000002ae165b (anonymous namespace)::MachineVerifierLegacyPass::runOnMachineFunction(llvm::MachineFunction&) MachineVerifier.cpp:0:0
 #9 0x00000000029da923 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x29da923)
#10 0x0000000002f48d23 llvm::FPPassManager::runOnFunction(llvm::Function&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2f48d23)
#11 0x0000000002f4f751 llvm::FPPassManager::runOnModule(llvm::Module&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2f4f751)
#12 0x0000000002f4942d llvm::legacy::PassManagerImpl::run(llvm::Module&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2f4942d)
...

```

</details>

https://github.com/llvm/llvm-project/pull/125219