When providing a code completion for an Objective-C message send, drop

When providing a code completion for an Objective-C message send, drop
the parameter names from the completions, e.g., provide

  withString:(NSString *)

instead of

  withString:(NSString *)string

since the parameter name is, by convention, redundant with the
selector piece that precedes it and the completions can get
unnecessarily long.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112456 91177308-0d34-0410-b5e6-96231b3b80d8