Remove unnecessary LLVMRustPersonalityFn binding

LLVM Core C bindings provide this function for all the versions back to what we support (3.7), and
helps to avoid this unnecessary builder->function transition every time. Also a negative diff.

src/rustllvm/RustWrapper.cpp

@@ -1082,14 +1082,6 @@ extern "C" void LLVMRustAddHandler(LLVMValueRef CatchSwitchRef,
 #endif
 }
 
-extern "C" void LLVMRustSetPersonalityFn(LLVMBuilderRef B,
-                                         LLVMValueRef Personality) {
-#if LLVM_VERSION_GE(3, 8)
-  unwrap(B)->GetInsertBlock()->getParent()->setPersonalityFn(
-      cast<Function>(unwrap(Personality)));
-#endif
-}
-
 #if LLVM_VERSION_GE(3, 8)
 extern "C" OperandBundleDef *LLVMRustBuildOperandBundleDef(const char *Name,
                                                            LLVMValueRef *Inputs,