Inline the newProverEnvironment methods of FormulaManagerFactory
in the Solver class.
Production code uses the Solver class anyway,
and test code can use the methods directly on the FormulaManager.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14910 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c