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/sendfile.h b/libc/include/sys/sendfile.h
index 4b00d5d..e1a34d2 100644
--- a/libc/include/sys/sendfile.h
+++ b/libc/include/sys/sendfile.h
@@ -40,15 +40,13 @@
 
 /* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
 #if defined(__USE_FILE_OFFSET64)
-ssize_t sendfile(int __out_fd, int __in_fd, off_t* _Nullable __offset, size_t __count) __RENAME(sendfile64) __INTRODUCED_IN(21);
+ssize_t sendfile(int __out_fd, int __in_fd, off_t* _Nullable __offset, size_t __count) __RENAME(sendfile64);
 #else
 /**
  * [sendfile(2)](http://man7.org/linux/man-pages/man2/sendfile.2.html) copies data directly
  * between two file descriptors.
  *
  * Returns the number of bytes copied on success, and returns -1 and sets `errno` on failure.
- *
- * Available since API level 21.
  */
 ssize_t sendfile(int __out_fd, int __in_fd, off_t* _Nullable __offset, size_t __count);
 #endif
@@ -57,6 +55,6 @@
  * Like sendfile() but allows using a 64-bit offset
  * even from a 32-bit process without `__FILE_OFFSET_BITS=64`.
  */
-ssize_t sendfile64(int __out_fd, int __in_fd, off64_t* _Nullable __offset, size_t __count) __INTRODUCED_IN(21);
+ssize_t sendfile64(int __out_fd, int __in_fd, off64_t* _Nullable __offset, size_t __count);
 
 __END_DECLS