[analyzer] NFC: RetainCountChecker: Don't dump() symbols into program point tags.

We don't need a separate node for every symbol, because whenever the first
symbol leaks, a bug is emitted, the analysis is sinked, and the checker
callback immediately returns due to State variable turning into null,
so we never get to see the second leaking symbol.

Additionally, we are no longer able to break normal analysis while experimenting
with debug dumps.

Differential Revision: https://reviews.llvm.org/D52804

llvm-svn: 344538