Switch to an idiomatic C++ erase/remove for this loop, and fix a bug in the
process (I don't believe it's possible to write a testcase for the bug with
a non-checking STL implementation).
Objective-C properties. Fixes a crash in Sema where RHS of
the property assignment is an lvalue for an incomplete type.
// rdar://15118128. Reviewed offline by John McCall.