libc: remove reference to non-existent readme

remove reference to non-existent readme in libc.

Pointing to the documentation page doesn't make sense in this case,
because it doesn't explain the use of `#undef XXX` for this case anyway.

Signed-off-by: raiden00pl <raiden00@railab.me>

include/strings.h

@@ -44,15 +44,15 @@
  * IEEE Std 1003.1-2008
  */
 
-#ifndef bcmp /* See mm/README.txt */
+#ifndef bcmp
 #define bcmp(b1,b2,len)  memcmp(b1,b2,(size_t)len)
 #endif
 
-#ifndef bcopy /* See mm/README.txt */
+#ifndef bcopy
 #define bcopy(b1,b2,len) memmove(b2,b1,len)
 #endif
 
-#ifndef bzero /* See mm/README.txt */
+#ifndef bzero
 #define bzero(s,n)       memset(s,0,n)
 #endif