RuntimeLibcalls: Remove darwin override of half convert libcalls (#148782)

These are already the default calls set for these conversions, so
they should not require explicit setting. The non-default cases are
currently overridden in ARMISelLowering. Just delete this until
the list of calls and lowering decisions are separated.

This was added back in 6402ad2. It
appears to not be relevant for AArch64, where calls appear to never
be used for these. It also appears to not be relevant for x86, where
the default calls seem to always end up used anyway.

Author: arsenm

llvm/lib/IR/RuntimeLibcalls.cpp

@@ -78,15 +78,6 @@ void RuntimeLibcallsInfo::initLibcalls(const Triple &TT,
       setLibcallImpl(RTLIB::UNWIND_RESUME, RTLIB::_Unwind_SjLj_Resume);
   }
 
-  // A few names are different on particular architectures or environments.
-  if (TT.isOSDarwin()) {
-    // For f16/f32 conversions, Darwin uses the standard naming scheme,
-    // instead of the gnueabi-style __gnu_*_ieee.
-    // FIXME: What about other targets?
-    setLibcallImpl(RTLIB::FPEXT_F16_F32, RTLIB::__extendhfsf2);
-    setLibcallImpl(RTLIB::FPROUND_F32_F16, RTLIB::__truncsfhf2);
-  }
-
   if (TT.isOSOpenBSD()) {
     setLibcallImpl(RTLIB::STACKPROTECTOR_CHECK_FAIL, RTLIB::Unsupported);
     setLibcallImpl(RTLIB::STACK_SMASH_HANDLER, RTLIB::__stack_smash_handler);