Remove the always-true __INTRODUCED_IN() annotations.

The NDK no longer supports API levels earlier than 21.

This *doesn't* include <ctype.h> because I have a separate change
rewriting that (that's blocked on the upcoming libc++ update).

Test: treehugger
Change-Id: I53e915f27011dfc0513e0c78d8799377e183ceca
diff --git a/libc/include/locale.h b/libc/include/locale.h
index 27f2a3f..6100765 100644
--- a/libc/include/locale.h
+++ b/libc/include/locale.h
@@ -98,11 +98,11 @@
 
 struct lconv* _Nonnull localeconv(void) __INTRODUCED_IN_NO_GUARD_FOR_NDK(21);
 
-locale_t _Nullable duplocale(locale_t _Nonnull __l) __INTRODUCED_IN(21);
-void freelocale(locale_t _Nonnull __l) __INTRODUCED_IN(21);
-locale_t _Nullable newlocale(int __category_mask, const char* _Nonnull __locale_name, locale_t _Nullable __base) __INTRODUCED_IN(21);
+locale_t _Nullable duplocale(locale_t _Nonnull __l);
+void freelocale(locale_t _Nonnull __l);
+locale_t _Nullable newlocale(int __category_mask, const char* _Nonnull __locale_name, locale_t _Nullable __base);
 char* _Nullable setlocale(int __category, const char* _Nullable __locale_name);
-locale_t _Nullable uselocale(locale_t _Nullable __l) __INTRODUCED_IN(21);
+locale_t _Nullable uselocale(locale_t _Nullable __l);
 
 #define LC_GLOBAL_LOCALE __BIONIC_CAST(reinterpret_cast, locale_t, -1L)