[SYCL] Remove aspect-ext_oneapi_bfloat16_math_functions

[JackAKirk]

It doesn't look like aspect-ext_oneapi_bfloat16_math_functions has any purpose at all since all bfloat16 math functions now have generic implementations. I think we can probably remove it and then set this test to run generically:

https://github.com/intel/llvm/blob/453ffdcf41dd50ec66b5cc9ea6304fadd10f18e8/sycl/test-e2e/BFloat16/bfloat16_builtins.cpp#L1

@jinge90 do you think this makes sense?

[steffenlarsen]

Ping @jinge90 on the question above.

[jinge90]

Hi, @steffenlarsen and @JackAKirk Yes, for "non-cuda" targets, we just use generic fp32 math functions to implement these bf16 functions, they can run on any device. Thanks very much.

[steffenlarsen]

https://github.com/intel/llvm/pull/13696 should address this.