Update contrib/trgm_regexp's memory management.

While no code change was necessary for this code to keep working, we
don't need to use PG_TRY()/PG_FINALLY() with explicit clean-up while
working with regexes anymore.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKGK3PGKwcKqzoosamn36YW-fsuTdOPPF1i_rtEO%3DnEYKSg%40mail.gmail.com

contrib/pg_trgm/trgm_regexp.c

@@ -549,22 +549,9 @@ createTrgmNFA(text *text_re, Oid collation,
 			   REG_ADVANCED | REG_NOSUB, collation);
 #endif
 
-	/*
-	 * Since the regexp library allocates its internal data structures with
-	 * malloc, we need to use a PG_TRY block to ensure that pg_regfree() gets
-	 * done even if there's an error.
-	 */
-	PG_TRY();
-	{
 	trg = createTrgmNFAInternal(&regex, graph, rcontext);
-	}
-	PG_FINALLY();
-	{
-		pg_regfree(&regex);
-	}
-	PG_END_TRY();
 
-	/* Clean up all the cruft we created */
+	/* Clean up all the cruft we created (including regex) */
 	MemoryContextSwitchTo(oldcontext);
 	MemoryContextDelete(tmpcontext);