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/sys/vfs.h b/libc/include/sys/vfs.h
index 18ae428..3579799 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -105,9 +105,9 @@
 #define XFS_SUPER_MAGIC       0x58465342
 
 int statfs(const char* _Nonnull __path, struct statfs* _Nonnull __buf);
-int statfs64(const char* _Nonnull __path, struct statfs64* _Nonnull __buf) __INTRODUCED_IN(21);
+int statfs64(const char* _Nonnull __path, struct statfs64* _Nonnull __buf);
 int fstatfs(int __fd, struct statfs* _Nonnull __buf);
-int fstatfs64(int __fd, struct statfs64* _Nonnull __buf) __INTRODUCED_IN(21);
+int fstatfs64(int __fd, struct statfs64* _Nonnull __buf);
 
 __END_DECLS