remove volatile qualification from category pointers in __locale_struct

commit 63c188ec42e76ff768e81f6b65b11c68fc43351e missed making this
change when switching from atomics to locking for modification of the
global locale, leaving access to locale structures unnecessarily
burdened with the restrictions of volatile.

the volatile qualification was originally added in commit
56fbaa3bbe73f12af2bfbbcf2adb196e6f9fe264.

src/internal/libc.h

@@ -8,7 +8,7 @@
 struct __locale_map;
 
 struct __locale_struct {
-	const struct __locale_map *volatile cat[6];
+	const struct __locale_map *cat[6];
 };
 
 struct tls_module {