In the release notes for the next release, mention that pragmas that
specify a predicate or a function now need a pred() or func() wrapper,
and that pragmas without such wrappers now get a warning, which can be
shut up (in that release) with --no-warn-potentially-ambiguous-pragma.
After the release, upgrade the warning to an error. In the release
after that, remove the option, and always generate an error.

After the release, delete from io.m the predicates that simply forward
the work to one of the submodules we carved off io.m years ago.

After the release, delete getopt_io.m, and the make rules that construct
getopt.m from it.

For each of the quoted-x-flag options, delete its original x-flag version.

Delete the --warn-interface-imports option name synonym.