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/arch-mips/string/memchr.c b/libc/arch-mips/string/memchr.c
index 6b4c8cc..bc24f79 100644
--- a/libc/arch-mips/string/memchr.c
+++ b/libc/arch-mips/string/memchr.c
@@ -100,7 +100,7 @@
 }
 
 void *
-memchr (void const *s, int c_in, size_t n) __overloadable
+memchr (void const *s, int c_in, size_t n)
 {
   if (n != 0) {
     const unsigned char *p = (const unsigned char *) s;