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/unistd.h b/libc/include/unistd.h
index 7ad94e1..98fab52 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -86,12 +86,12 @@
 pid_t  getppid(void);
 pid_t  getpgrp(void);
 int    setpgrp(void);
-pid_t  getsid(pid_t __pid) __INTRODUCED_IN(17);
+pid_t  getsid(pid_t __pid);
 pid_t  setsid(void);
 
 int execv(const char* _Nonnull __path, char* _Nullable const* _Nullable __argv);
 int execvp(const char* _Nonnull __file, char* _Nullable const* _Nullable __argv);
-int execvpe(const char* _Nonnull __file, char* _Nullable const* _Nullable __argv, char* _Nullable const* _Nullable __envp) __INTRODUCED_IN(21);
+int execvpe(const char* _Nonnull __file, char* _Nullable const* _Nullable __argv, char* _Nullable const* _Nullable __envp);
 int execve(const char* _Nonnull __file, char* _Nullable const* _Nullable __argv, char* _Nullable const* _Nullable __envp);
 int execl(const char* _Nonnull __path, const char* _Nullable __arg0, ...) __attribute__((__sentinel__));
 int execlp(const char* _Nonnull __file, const char* _Nullable __arg0, ...) __attribute__((__sentinel__));
@@ -206,7 +206,7 @@
 int access(const char* _Nonnull __path, int __mode);
 int faccessat(int __dirfd, const char* _Nonnull __path, int __mode, int __flags);
 int link(const char* _Nonnull __old_path, const char* _Nonnull __new_path);
-int linkat(int __old_dir_fd, const char* _Nonnull __old_path, int __new_dir_fd, const char* _Nonnull __new_path, int __flags) __INTRODUCED_IN(21);
+int linkat(int __old_dir_fd, const char* _Nonnull __old_path, int __new_dir_fd, const char* _Nonnull __new_path, int __flags);
 int unlink(const char* _Nonnull __path);
 int unlinkat(int __dirfd, const char* _Nonnull __path, int __flags);
 int chdir(const char* _Nonnull __path);
@@ -218,10 +218,9 @@
 #endif
 int chroot(const char* _Nonnull __path);
 int symlink(const char* _Nonnull __old_path, const char* _Nonnull __new_path);
-int symlinkat(const char* _Nonnull __old_path, int __new_dir_fd, const char* _Nonnull __new_path) __INTRODUCED_IN(21);
+int symlinkat(const char* _Nonnull __old_path, int __new_dir_fd, const char* _Nonnull __new_path);
 ssize_t readlink(const char* _Nonnull __path, char* _Nonnull __buf, size_t __buf_size);
-ssize_t readlinkat(int __dir_fd, const char* _Nonnull __path, char* _Nonnull __buf, size_t __buf_size)
-    __INTRODUCED_IN(21);
+ssize_t readlinkat(int __dir_fd, const char* _Nonnull __path, char* _Nonnull __buf, size_t __buf_size);
 int chown(const char* _Nonnull __path, uid_t __owner, gid_t __group);
 int fchown(int __fd, uid_t __owner, gid_t __group);
 int fchownat(int __dir_fd, const char* _Nonnull __path, uid_t __owner, gid_t __group, int __flags);
@@ -261,13 +260,13 @@
 
 int dup(int __old_fd);
 int dup2(int __old_fd, int __new_fd);
-int dup3(int __old_fd, int __new_fd, int __flags) __INTRODUCED_IN(21);
+int dup3(int __old_fd, int __new_fd, int __flags);
 int fsync(int __fd);
 int fdatasync(int __fd);
 
 /* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
 #if defined(__USE_FILE_OFFSET64)
-int truncate(const char* _Nonnull __path, off_t __length) __RENAME(truncate64) __INTRODUCED_IN(21);
+int truncate(const char* _Nonnull __path, off_t __length) __RENAME(truncate64);
 off_t lseek(int __fd, off_t __offset, int __whence) __RENAME(lseek64);
 ssize_t pread(int __fd, void* _Nonnull __buf, size_t __count, off_t __offset) __RENAME(pread64);
 ssize_t pwrite(int __fd, const void* _Nonnull __buf, size_t __count, off_t __offset) __RENAME(pwrite64);
@@ -280,7 +279,7 @@
 int ftruncate(int __fd, off_t __length);
 #endif
 
-int truncate64(const char* _Nonnull __path, off64_t __length) __INTRODUCED_IN(21);
+int truncate64(const char* _Nonnull __path, off64_t __length);
 off64_t lseek64(int __fd, off64_t __offset, int __whence);
 ssize_t pread64(int __fd, void* _Nonnull __buf, size_t __count, off64_t __offset);
 ssize_t pwrite64(int __fd, const void* _Nonnull __buf, size_t __count, off64_t __offset);
@@ -303,7 +302,7 @@
 
 int acct(const char* _Nullable __path);
 
-int getpagesize(void) __INTRODUCED_IN(21);
+int getpagesize(void);
 
 long syscall(long __number, ...);