Revert "ppc: [liftoff] implement DropStackSlotsAndRet"

This reverts commit d7c9b31a.

Reason for revert: investigating intermittent failures on `test/mjsunit/wasm/parallel_compilation.js`

Original change's description:
> ppc: [liftoff] implement DropStackSlotsAndRet
>
> Change-Id: I05bcba3ad27b46b7c7888940895605ad463fc960
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3155302
> Reviewed-by: Milad Fa <mfarazma@redhat.com>
> Commit-Queue: Junliang Yan <junyan@redhat.com>
> Cr-Commit-Position: refs/heads/main@{#76774}

Change-Id: I19452e75aad78b446ac6e2cd8b80cec4d792671f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3202471Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#77221}

src/wasm/baseline/ppc/liftoff-assembler-ppc.h

@@ -2738,8 +2738,7 @@ void LiftoffAssembler::RecordSpillsInSafepoint(Safepoint& safepoint,
 }
 
 void LiftoffAssembler::DropStackSlotsAndRet(uint32_t num_stack_slots) {
-  Drop(num_stack_slots);
-  Ret();
+  bailout(kUnsupportedArchitecture, "DropStackSlotsAndRet");
 }
 
 void LiftoffAssembler::CallC(const ValueKindSig* sig,