This MR gets rid of the pattern synonym error recovery mechanism
recoverPSB). The rationale is that the fake pattern synonym binding
that the recovery mechanism introduced could lead to undesirable
knock-on errors, and it isn't really feasible to conjure up a
satisfactory binding as pattern synonyms can be used both in expressions
It isn't such a big deal to eagerly fail compilation on a pattern synonym that doesn't typecheck anyway.
Accept test changes.