onnxruntime

Remove fp16 support from apple (#15270)

### Description

Removing fp16 support from apple build


### Motivation and Context
FP16 support on ARM64 only available after armv8.2a, thus the clang
compiler needs a compilation flag `-march=armv8.2-a+fp16`.
Unfortunately, our current universal build does not support hardware
specific compilation flags on cpp source files, as it would cause
trouble when compiling against more than one hardware target. Until we
figure out how to remove this limitation, had to disable fp16 support
for Apple systems.