Don't try to typo-correct 'super' in an objc method.

This created 2 issues:

1) Performance issue, since typo-correction with PCH/modules is rather expensive.
2) Correctness issue, since if it managed to "correct" 'super' then bogus compiler errors would
be emitted, like this:

3.m:8:3: error: unknown type name 'super'; did you mean 'super1'?
  super.x = 0;
  ^~~~~
  super1
t3.m:5:13: note: 'super1' declared here
typedef int super1;
            ^
t3.m:8:8: error: expected identifier or '('
  super.x = 0;
       ^

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177126 91177308-0d34-0410-b5e6-96231b3b80d8