[ARM] Remove duplicate fp16 intrinsics

These vdup and vmov float16 intrinsics are being defined in both the
general section and then again in fp16 under a !aarch64 flag. The
vdup_lane intrinsics were being defined in both aarch64 and !aarch64
sections, so have been commoned.  They are defined as macros, so do not
give duplicate warnings, but removing the duplicates shouldn't alter the
available intrinsics.