libc: remove bcmp prototype

AFAIK, bionic only ever provided an implementation of bcmp
for x86, and even then, the code was never actually compiled.
Remove the prototype.

bcmp() has been obsoleted and replaced by memcmp()

Change-Id: I549d02ab6a9241a9acbbbfade0d98a9a02c2eaee

libc/include/strings.h

@@ -43,7 +43,6 @@
 #include <sys/cdefs.h>
 
 __BEGIN_DECLS
-int	 bcmp(const void *, const void *, size_t);
 void	 bcopy(const void *, void *, size_t);
 void	 bzero(void *, size_t);
 int	 ffs(int);