Remove a tautology from <bits/threads_inlines.h>.

The next NDK to take these headers only supports API 21 and later.

Test: treehugger
Change-Id: I31a07842a498e818ec8f16c217c365b100a5e05b
diff --git a/libc/include/bits/threads_inlines.h b/libc/include/bits/threads_inlines.h
index afaed64..17de4a1 100644
--- a/libc/include/bits/threads_inlines.h
+++ b/libc/include/bits/threads_inlines.h
@@ -103,12 +103,10 @@
   return __bionic_thrd_error(pthread_mutex_lock(__mtx));
 }
 
-#if __ANDROID_API__ >= 21
 __BIONIC_THREADS_INLINE int mtx_timedlock(mtx_t* __mtx,
                                           const struct timespec* __timeout) {
   return __bionic_thrd_error(pthread_mutex_timedlock(__mtx, __timeout));
 }
-#endif
 
 __BIONIC_THREADS_INLINE int mtx_trylock(mtx_t* __mtx) {
   return __bionic_thrd_error(pthread_mutex_trylock(__mtx));