whack down the smartmatch table

The semantics of smartmatches should largely be inferable from the
X argument, and should not imply heavy run-time processing of the
X value.  In general, smartmatches should not be providing implicit
any/all semantics except in a few cases where no other interpretation
is possible.  Since we now have Sets, Hash smartmatch no longer needs
to emulate sets, and can be eqv identity.  Regex on LHS now considered
too magical, but we provide provide Callable escape value for reverse
match of Associative and Positional.  (Reverse Regex match on keys
can be written { .keys.any ~~ /.../ } ~~ %hash for instance.)