Remove all traces of tuplestore_donestoring() in the C code

Remove all traces of tuplestore_donestoring() in the C code

This routine is a no-op since dd04e95 from 2003, with a macro kept
around for compatibility purposes.  This has led to the same code
patterns being copy-pasted around for no effect, sometimes in confusing
ways like in pg_logical_slot_get_changes_guts() from logical.c where the
code was actually incorrect.

This issue has been discussed on two different threads recently, so
rather than living with this legacy, remove any uses of this routine in
the C code to simplify things.  The compatibility macro is kept to avoid
breaking any out-of-core modules that depend on it.

Reported-by: Tatsuhito Kasahara, Justin Pryzby
Author: Tatsuhito Kasahara
Discussion: https://postgr.es/m/20211217200419.GQ17618@telsasoft.com
Discussion: https://postgr.es/m/CAP0=ZVJeeYfAeRfmzqAF2Lumdiv4S4FewyBnZd4DPTrsSQKJKw@mail.gmail.com