Revert "[AArch64] Add ARMv8.2-A FP16 vefctor intrinsics"

This reverts commit r304493. It breaks all the Darwin bots:
http://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-incremental_check/37168

Failure:
Failing Tests (2):
    Clang :: CodeGen/aarch64-v8.2a-neon-intrinsics.c
    Clang :: CodeGen/arm_neon_intrinsics.c

llvm-svn: 304509