Fix some unused-variable warnings.

A test-build with a modern clang points out a number of 'set but not
used' variables, which clang seems to have got better at recently.

In cases where there's conditioned-out or commented-out code using the
variable, I've left it in and added a warning-suppressing cast to
void. Otherwise I've just deleted the variables.

palisade.c

@@ -634,8 +634,6 @@ static char *new_game_desc(const game_params *params, random_state *rs,
     DSF *dsf = NULL;
     int i, r, c;
 
-    int attempts = 0;
-
     for (i = 0; i < wh; ++i) shuf[i] = i;
     xshuffle(shuf, wh, rs);
 
@@ -646,7 +644,6 @@ static char *new_game_desc(const game_params *params, random_state *rs,
     soln[wh] = '\0';
 
     do {
-        ++attempts;
         setmem(soln, '@', wh);
 
         dsf_free(dsf);