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-arm/generic/bionic/strlen.c b/libc/arch-arm/generic/bionic/strlen.c
index dccd564..44bd72f 100644
--- a/libc/arch-arm/generic/bionic/strlen.c
+++ b/libc/arch-arm/generic/bionic/strlen.c
@@ -29,7 +29,7 @@
 #include <string.h>
 #include <stdint.h>
 
-size_t strlen(const char *s) __overloadable
+size_t strlen(const char *s)
 {
     __builtin_prefetch(s);
     __builtin_prefetch(s+32);