[analyzer] SelfInit: Stop tracking self if it's assigned a value we

don't reason about.

Self is just like a local variable in init methods, so it can be
assigned anything like result of static functions, other methods ... So
to suppress false positives that result in such cases, stop tracking the
checker-specific state after self is being assigned to (unless the
value is't being assigned to is either self or conforms to our rules).

This change does not invalidate any existing regression tests.

llvm-svn: 156420