[MC] Remove an unneeded Darwin x86_64 workaround

The workaround (relocation suppression) from
7b46bb8 (2011) has been unneeded after
bfd0f01 (2014) removed
`if (!A_base) return false;` and `if (!B_base) return false;`

Author: MaskRay

llvm/lib/MC/MachObjectWriter.cpp

@@ -710,16 +710,6 @@ bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
         return false;
       return true;
     }
-    // For Darwin x86_64, there is one special case when the reference IsPCRel.
-    // If the fragment with the reference does not have a base symbol but meets
-    // the simple way of dealing with this, in that it is a temporary symbol in
-    // the same atom then it is assumed to be fully resolved.  This is needed so
-    // a relocation entry is not created and so the static linker does not
-    // mess up the reference later.
-    else if(!FB.getAtom() &&
-            SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
-      return true;
-    }
   }
 
   // If they are not in the same section, we can't compute the diff.