Don't attempt pattern synonym error recovery

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 and patterns.

It isn't such a big deal to eagerly fail compilation on a pattern synonym that doesn't typecheck anyway.

TODO:

• Accept test changes.