Deprecate ToWorkingIR (#2028)

* Deprecate firrtl.passes.ToWorkingIR

Deprecate ToWorkingIR as it is now an identity transform.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

* Deprecate firrtl.stage.Forms.WorkingIR

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

* Switch from Forms.WorkingIR to Forms.MinimalHighForm

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

Co-authored-by: Jack Koenig <koenig@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>