[MLIR][Affine][Analysis] Merge FAC and FACV

With the introduction of IntegerPolyhedron and IntegerRelation in Presburger
directory, the purpose of FlatAffineConstraints becomes redundant. For users
requiring Presburger arithmetic without IR information, Presburger library can
directly be used. For users requiring IR information,
FlatAffineValueConstraints can be used.

This patch merges FAC and FACV to remove redundancy of FAC.

Reviewed By: arjunp

Differential Revision: https://reviews.llvm.org/D122476