Remove the name of the function return variable
from AbstractStateWithAssumptions.getAsAssumeEdges().
Now that we have a common name for these pseudo variables
defined in the CFA, we do not need a parameter to specify it
(plus, neither the one implementor nor the callers of this method
ever bothered to use it).

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14493 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c