Avoid VACUUM FULL altogether in initdb.

Commit ed7b3b3811 purported to remove initdb's use of VACUUM FULL,
as had been agreed to in a pghackers discussion back in Dec 2014.
But it missed this one ...

src/bin/initdb/initdb.c

@@ -2130,7 +2130,7 @@ make_template0(FILE *cmdfd)
 		/*
 		 * Finally vacuum to clean up dead rows in pg_database
 		 */
-		"VACUUM FULL pg_database;\n\n",
+		"VACUUM pg_database;\n\n",
 		NULL
 	};