[MLIR][Presburger] Refactor subtraction in preparation for making it iterative

Refactor the operation of subtraction by
- removing the usage of SimplexRollbackScopeExit since this
  can't be used in the iterative version
- reducing the number of stack variables to make the
  iterative version easier to follow

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D123156