[AMDGPU] remove unused AssemblerPredicates

An internal build is hitting asserts complaining about too many subtarget
features:
  llvm/utils/TableGen/Types.cpp:42:
    const char* llvm::getMinimalTypeForEnumBitfield(uint64_t):
    Assertion `MaxIndex <= 64 && "Too many bits"' failed.

  llvm/utils/TableGen/AsmMatcherEmitter.cpp:1476:
    void {anonymous}::AsmMatcherInfo::buildInfo():
    Assertion `SubtargetFeatures.size() <= 64 && "Too many subtarget features!"'
    failed.

The short-term solution is to remove a few unused AssemblerPredicates to get
under the limit.

The long-term solution seems to be to revisit these asserts. E.g., rather than
hardcoded '64', use the standard sized std::bitset like the other places that
track subtarget features.

Differential Revision: https://reviews.llvm.org/D58516

llvm-svn: 354604