Fix assertion failure in thread safety analysis (PR34800).

Summary:
Fix an assertion failure (http://llvm.org/PR34800) and clean up unused code relevant to the fixed logic.

A bit of context: when `SExprBuilder::translateMemberExpr` is called on a member expression that involves a conversion operator, for example, `til::Project` constructor can't just call `getName()` on it, since the name is not a simple identifier. In order to handle this case I've introduced an optional string to print the member name to. I discovered that the other two `til::Project` constructors are not used, so it was better to delete them instead of ensuring they work correctly with the new logic.

Reviewers: aaron.ballman

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D38458

llvm-svn: 314895