Remove __overloadable/__RENAME_CLANG

Now that we have a clang that supports transparent overloads, we can
kill all of this cruft, and restore our upstream sources to their
untouched glory. Woohoo!

Bug: 12231437
Test: Built aosp_marlin; no obvious patch-related aosp_mips issues.
Change-Id: I520a19d014f12137f80e43f973dccd6711c571cd
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index 14b5224..6fce0a5 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -165,7 +165,7 @@
 int stat64(const char* __path, struct stat64* __buf) __INTRODUCED_IN(21);
 
 int mknod(const char* __path, mode_t __mode, dev_t __dev);
-mode_t umask(mode_t __mask) __overloadable __RENAME_CLANG(umask);
+mode_t umask(mode_t __mask);
 
 #if defined(__BIONIC_INCLUDE_FORTIFY_HEADERS)
 #include <bits/fortify/stat.h>