Get rid of minimallyEncoded* prefix for validators

Summary:
As of D10805, we no longer have any MinimallyEncoded* types. In some of the diffs that removed the prefix from the types I also removed the prefix from the corresponding validator name.. in some cases I didn't. This diff removes the prefix from validators where it remains.

Depends on D10805

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D10806