Remove method for PathFormula comparison
from PredicateAbstractionManager
that was unused for 2 years (since r5983).
It relied on a crude and ugly hack,
looking into the syntactic structure of PathFormulas.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13575 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c