Clang importer: remove support for implicit properties.

We decided not to support "implicit" properties, where we import
getter/setter pairs as properties. Rather, we only import a property
when there is an explicit "@property" in Objective-C. Remove the flag
and supporting code for implicit properties.

lib/Frontend/CompilerInvocation.cpp

@@ -808,9 +808,6 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts,
     });
   }
 
-  Opts.InferImplicitProperties |=
-    Args.hasArg(OPT_enable_objc_implicit_properties);
-
   Opts.OmitNeedlessWords |= Args.hasArg(OPT_enable_omit_needless_words);
   Opts.InferDefaultArguments |= Args.hasArg(OPT_enable_infer_default_arguments);