op.c: Use new feature bundle hints

op.c: Use new feature bundle hints

Now ‘use v5.22’ and ‘use 5.005’ no longer have to load feature.pm
to enable the current feature bundle.  All they do is twiddle bits
in PL_hints.

Since version declarations no longer call feature->unimport, there
may be junk left over in %^H (which we leave for speed’s sake), so
feature.pm has to delete that junk before enabling features.