PPC: Revert "[wasm-simd] Add bitmask to SIMD MVP"

Port 2f7f90b5

Original Commit Message:

    This reverts commit dfbbb4a5.

    Reason for revert: Bitmask added post 84 cut, so it is not part of origin trial. Therefore it is still a post-mvp.

    Original change's description:
    > [wasm-simd] Add bitmask to SIMD MVP
    >
    > This removes the post-mvp flag for bitmask, since it was accepted into
    > the proposal, see https://github.com/WebAssembly/simd/pull/201.
    >
    > Bug: v8:10308
    > Change-Id: I4ced43a6484660125d773bc9de46bdea9f72b13b
    > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2216532
    > Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
    > Commit-Queue: Zhi An Ng <zhin@chromium.org>
    > Cr-Commit-Position: refs/heads/master@{#67993}

R=zhin@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I2076f24c2e232ca071b9dc62c9f23d3eb7acfa72
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2233406Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#68219}

src/compiler/backend/ppc/instruction-selector-ppc.cc

@@ -2212,12 +2212,6 @@ SIMD_BINOP_LIST(SIMD_VISIT_BINOP)
 #undef SIMD_BINOP_LIST
 #undef SIMD_TYPES
 
-void InstructionSelector::VisitI32x4BitMask(Node* node) { UNIMPLEMENTED(); }
-
-void InstructionSelector::VisitI16x8BitMask(Node* node) { UNIMPLEMENTED(); }
-
-void InstructionSelector::VisitI8x16BitMask(Node* node) { UNIMPLEMENTED(); }
-
 void InstructionSelector::VisitI32x4Shl(Node* node) { UNIMPLEMENTED(); }
 
 void InstructionSelector::VisitI32x4ShrS(Node* node) { UNIMPLEMENTED(); }