Replace the SimpleMap used by CFASingleLoopTransformation
which was only used for revertible map changes in a single place
by normal maps, which are copied when they need to be reverted.
This is slightly more inefficient, but hopefully not relevant,
and has simpler code.
If we need more efficiency, we should switch to PersistentSortedMaps,
or CopyOnWriteSortedMap.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13521 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c