* hash-table.h (remove_elt_with_hash): Return if slot is NULL rather
	than if is_empty (*slot).
	* hash-set-tests.c (test_set_of_strings): Add tests for addition of
	existing elt and for elt removal.
	* hash-map-tests.c (test_map_of_strings_to_int): Add test for removal
	of already removed elt.

	* hashtab.c (htab_remove_elt_with_hash): Return if slot is NULL rather
	than if *slot is HTAB_EMPTY_ENTRY.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r269695