[llvm] [AMDGPU] Remove unnecessary untieRegOperand (PR #107695)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-x86_64-debian-fast` 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/56/builds/6805

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

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: LLVM :: tools/llvm-reduce/remove-instructions.ll (80056 of 80066)
PASS: lit :: googletest-timeout.py (80057 of 80066)
PASS: lit :: selecting.py (80058 of 80066)
PASS: lit :: shtest-timeout.py (80059 of 80066)
PASS: LLVM-Unit :: Support/./SupportTests/127/173 (80060 of 80066)
PASS: lit :: max-time.py (80061 of 80066)
PASS: lit :: shtest-shell.py (80062 of 80066)
PASS: lit :: shtest-define.py (80063 of 80066)
PASS: LLVM-Unit :: Support/./SupportTests/125/173 (80064 of 80066)
PASS: LLVM :: tools/llvm-reduce/parallel-workitem-kill.ll (80065 of 80066)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1415.449462

```

</details>

https://github.com/llvm/llvm-project/pull/107695