Revert temporal primary keys and foreign keys

Revert temporal primary keys and foreign keys

This feature set did not handle empty ranges correctly, and it's now
too late for PostgreSQL 17 to fix it.

The following commits are reverted:

    6db4598fcb8 Add stratnum GiST support function
    46a0cd4cefb Add temporal PRIMARY KEY and UNIQUE constraints
    86232a49a43 Fix comment on gist_stratnum_btree
    030e10ff1a3 Rename pg_constraint.conwithoutoverlaps to conperiod
    a88c800deb6 Use daterange and YMD in without_overlaps tests instead of tsrange.
    5577a71fb0c Use half-open interval notation in without_overlaps tests
    34768ee3616 Add temporal FOREIGN KEY contraints
    482e108cd38 Add test for REPLICA IDENTITY with a temporal key
    c3db1f30cba doc:  clarify PERIOD and WITHOUT OVERLAPS in CREATE TABLE
    144c2ce0cc7 Fix ON CONFLICT DO NOTHING/UPDATE for temporal indexes

Discussion: https://www.postgresql.org/message-id/d0b64a7a-dfe4-4b84-a906-c7dedfa40a3e@eisentraut.org