[analyzer] RetainCountChecker: don't track through xpc_connection_set_context.
It is unfortunate that we have to mark these exceptions in multiple places.
This was already in CallEvent. I suppose it does let us be more precise
about saying /which/ arguments have their retain counts invalidated -- the
connection's is still valid even though the context object's isn't -- but
we're not tracking the retain count of XPC objects anyway.
<rdar://problem/
13783514>
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180904
91177308-0d34-0410-b5e6-
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