kill strlen_user()

no callers, no consistent semantics, no sane way to use it...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/openrisc/include/asm/uaccess.h

@@ -264,7 +264,6 @@ clear_user(void *addr, unsigned long size)
 
 extern long strncpy_from_user(char *dest, const char __user *src, long count);
 
-extern __must_check long strlen_user(const char __user *str);
 extern __must_check long strnlen_user(const char __user *str, long n);
 
 #endif /* __ASM_OPENRISC_UACCESS_H */