Tighten short-circuit tests for deciding whether we need to invoke

Tighten short-circuit tests for deciding whether we need to invoke
tuptoaster.c --- fields that are compressed in-line are not a reason
to invoke the toaster.  Along the way, add a couple more htup.h macros
to eliminate confusing negated tests, and get rid of the already
vestigial TUPLE_TOASTER_ACTIVE symbol.