Reduce hash size for compute_array_stats, compute_tsvector_stats.

The size is only a hint, but a big hint chews up a lot of memory without
apparently improving performance much.

Analysis and patch by Noah Misch.

src/backend/tsearch/ts_typanalyze.c

@@ -186,7 +186,7 @@ compute_tsvector_stats(VacAttrStats *stats,
 	hash_ctl.match = lexeme_match;
 	hash_ctl.hcxt = CurrentMemoryContext;
 	lexemes_tab = hash_create("Analyzed lexemes table",
-							  bucket_width * 7,
+							  num_mcelem,
 							  &hash_ctl,
 					HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
 

src/backend/utils/adt/array_typanalyze.c

@@ -282,7 +282,7 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
 	elem_hash_ctl.match = element_match;
 	elem_hash_ctl.hcxt = CurrentMemoryContext;
 	elements_tab = hash_create("Analyzed elements table",
-							   bucket_width * 7,
+							   num_mcelem,
 							   &elem_hash_ctl,
 					HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);