Remove all "INTERFACE ROUTINES" style comments

Hi,

A number of postgres files have sections like heapam's

* INTERFACE ROUTINES
* relation_open - open any relation by relation OID
* relation_openrv - open any relation specified by a RangeVar
* relation_close - close any relation
* heap_open - open a heap relation by relation OID
* heap_openrv - open a heap relation specified by a RangeVar
* heap_close - (now just a macro for relation_close)
* heap_beginscan - begin relation scan
* heap_rescan - restart a relation scan
* heap_endscan - end relation scan
* heap_getnext - retrieve next tuple in scan
* heap_fetch - retrieve tuple with given tid
* heap_insert - insert tuple into a relation
* heap_multi_insert - insert multiple tuples into a relation
* heap_delete - delete a tuple from a relation
* heap_update - replace a tuple in a relation with another tuple
* heap_sync - sync heap, for when no WAL has been written

They're often out-of-date, and I personally never found them to be
useful. A few people, including yours truly, have been removing a few
here and there when overhauling a subsystem to avoid having to update
and then adjust them.

I think it might be a good idea to just do that for all at once. Having
to consider separately committing a removal, updating them without
fixing preexisting issues, or just leaving them outdated on a regular
basis imo is a usless distraction.

Comments?

Greetings,

Andres Freund