Revert "[analyzer] Break cycles (optionally) when trimming an ExplodedGraph."

The algorithm used here was ridiculously slow when a potential back-edge
pointed to a node that already had a lot of successors. The previous commit
makes this feature unnecessary anyway.

This reverts r177468 / f4cf6b10f863b9bc716a09b2b2a8c497dcc6aa9b.

Conflicts:

	lib/StaticAnalyzer/Core/BugReporter.cpp

llvm-svn: 177765