Remove remaining usages of `overload_on`

[dnezam]

There are still a few uses of overload_on in the codebase. Most of those should be removed, and perhaps a ban for overload_on[ introduced to catch unnecessary uses of overload in map or app.

A reasonable use of temp_overload_on can be found in arm7_target:

val () = List.app Parse.temp_overload_on
  (ListPair.zip
     (["EQ", "NE", "CS", "CC", "MI", "PL", "VS", "VC",
       "HI", "LS", "GE", "LT", "GT", "LE", "AL"],
      List.tabulate (15, fn i => wordsSyntax.mk_wordii (i, 4))))

To avoid merge conflicts, it is probably easiest to wait after #1214 has been merged.