[analyzer] RetainCountChecker: for now, do not trust the summaries of inlined code

Trusting summaries of inlined code would require a more thorough work,
as the current approach was causing too many false positives, as the new
example in test.  The culprit lies in the fact that we currently escape
all variables written into a field (but not passed off to unknown
functions!), which can result in inconsistent behavior.

rdar://45655344

Differential Revision: https://reviews.llvm.org/D53902

llvm-svn: 345746