Remove accumulator-based functions from the semantics

Ideally, auxiliary functions used in the semantics should have the simplest possible presentation, and not use accumulators.

E.g. `pat_bindings` currently has type `pat -> list varN -> list varN` but it should be `pat > list varN`.
There might be a few other occurrences.

No file or test is named. Search the semantics for accumulator-based auxiliary functions, starting with pat_bindings and its current pat -> list varN -> list varN type, then trace affected definitions and uses. Done means the identified auxiliary functions no longer require accumulator arguments and their semantics remain consistent.

Written by the indexing model from the issue text.