Fixes over-eager transforming when simplifying
Fixes over-eager transforming when simplifying

Fixes a problem when simplifying expressions where SymbolNodes in the
input expressions are incorrectly transformed, as if they were patterns
in the right-hand-side of the rule

josdejong/mathjs,FSMaxB/mathjs,josdejong/mathjs,josdejong/mathjs,FSMaxB/mathjs,josdejong/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,josdejong/mathjs