Convert MRSolver to use SAWCore rewriter instead of TermModel simulator backend

[brianhuffman]

Currently the MRSolver SAWScript commands internally use a term normalization procedure that is based on the TermModel backend of the SAWCore simulator. The kind of term normalization required here is exactly what the SAWCore rewriting engine was designed for, and we should convert MRSolver to use the SAWCore rewriter for this purpose.

On the other hand, the TermModel backend uses the SAWCore simulator in some unintended ways that interfere with some other refactoring efforts (#2429).

[sauclovian-g]

Mr. Solver has been removed, so this issue is no longer relevant.