Fix equivalence tests (#853)

* - modify firrtlEquivalenceTest to use yosys equiv_simple/equiv_induct instead of miter
- add RemoveValidIf pass to MinimumLowFirrtlOptimization

* add EquivalenceTest to FirrtlSpec.scala, make classes in IntegrationSpec.scala abstract

* change types of inputForm/outputForm to CircuitForm

* change EquivalenceTest message

* remove ICache equivalence tests

* fix rebase errors

* Add Ops scalatests to LEC suite

* Only run compiler-path-comparison LEC tests on Ops design

* Fixup issues with merge

Co-authored-by: Albert Magyar <albert.magyar@gmail.com>