Revert "[CodeGen] Mark fma as const for Android"

This code is intended to give a special exception for platforms which set errno in some math functions but not fma. This does not apply to Android, which does not set errno in any math functions (https://cs.android.com/android/platform/superproject/+/master:bionic/libc/include/math.h;drc=master;l=59). The correct implementation for Android is to set -fno-math-errno by default, which was done in https://reviews.llvm.org/D51068. Therefore, this special exception is no longer needed for Android. Deleting it slightly reduces code complexity, clang executable size, compile time, and test time.

This reverts fbfba29d.

Reviewed By: pirama

Differential Revision: https://reviews.llvm.org/D116755