Remove size parameter from dsf init and copy functions.

Now that the dsf knows its own size internally, there's no need to
tell it again when one is copied or reinitialised.

This makes dsf_init much more about *re*initialising a dsf, since now
dsfs are always allocated using a function that will initialise them
anyway. So I think it deserves a rename.

singles.c

@@ -439,7 +439,7 @@ static void connect_dsf(game_state *state, DSF *dsf)
 
     /* Construct a dsf array for connected blocks; connections
      * tracked to right and down. */
-    dsf_init(dsf, state->n);
+    dsf_reinit(dsf);
     for (x = 0; x < state->w; x++) {
         for (y = 0; y < state->h; y++) {
             i = y*state->w + x;