copy: remove reflinking debug message

It pretty much ends up in an inner loop most of the time, hence let's
just remove it. This is pretty easily debuggable with strace anyway...

src/basic/copy.c

@@ -163,8 +163,6 @@ int copy_bytes_full(
                                                 return 1; /* we copied only some number of bytes, which worked, but this means we didn't hit EOF, return 1 */
                                         }
                                 }
-
-                                log_debug_errno(r, "Reflinking didn't work, falling back to non-reflink copying: %m");
                         }
                 }
         }