[analyzer] Remove memoization from RunLoopAutoreleaseLeakChecker

Memoization dose not seem to be necessary, as other statement visitors
run just fine without it,
and in fact seems to be causing memory corruptions.
Just removing it instead of investigating the root cause.

rdar://45945002

Differential Revision: https://reviews.llvm.org/D54921

llvm-svn: 348822