[Sema][CodeComplete][ObjC] Don't include arrow/dot fixits

Summary:
Exempt ObjC from arrow/dot fixits since this has limited value for
Objective-C, where properties (referenced by dot syntax) are normally
backed by ivars (referenced by arrow syntax).

In addition, the current implementation doesn't properly mark
the fix it condition for Objective-C.

This was initially added in https://reviews.llvm.org/D41537
for C++ and then later C, don't believe the Objective-C changes
were intentional.

Reviewers: sammccall, yvvan

Subscribers: jfb, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D81263