Don't attempt pattern synonym error recovery

This commit 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.
See Note [Pattern synonym error recovery] in GHC.Tc.TyCl.PatSyn.

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

Fixes #23467