Remove unnecessary "DISTINCT" in psql's queries for \dAc and \dAf.

A moment's examination of these queries is sufficient to see that
they do not produce duplicate rows, unless perhaps there's
catalog corruption.  Using DISTINCT anyway is inefficient and
confusing; moreover it sets a poor example for anyone who
refers to psql -E output to see how to query the catalogs.

src/bin/psql/describe.c

@@ -6071,7 +6071,7 @@ listOperatorClasses(const char *access_method_pattern,
 	initPQExpBuffer(&buf);
 
 	printfPQExpBuffer(&buf,
-					  "SELECT DISTINCT"
+					  "SELECT\n"
 					  "  am.amname AS \"%s\",\n"
 					  "  pg_catalog.format_type(c.opcintype, NULL) AS \"%s\",\n"
 					  "  CASE\n"
@@ -6166,7 +6166,7 @@ listOperatorFamilies(const char *access_method_pattern,
 	initPQExpBuffer(&buf);
 
 	printfPQExpBuffer(&buf,
-					  "SELECT DISTINCT"
+					  "SELECT\n"
 					  "  am.amname AS \"%s\",\n"
 					  "  CASE\n"
 					  "    WHEN pg_catalog.pg_opfamily_is_visible(f.oid)\n"