Remove superfluous casts

-  Every non-const pointer converts automatically to void *.
-  Every pointer converts automatically to void *.
-  void * converts to any other pointer.
-  const void * converts to any other const pointer.
-  Integer variables convert to each other.

I changed the declaration of a few variables in order to allow removing
a cast.

However, I didn't attempt to edit casts inside comparisons, since they
are very delicate.  I also kept casts in variadic functions, since they
are necessary, and in allocation functions, because I have other plans
for them.

I also changed a few casts to int that are better as ptrdiff_t.

This change has triggered some warnings about const correctness issues,
which have also been fixed in this patch (see for example src/login.c).

Signed-off-by: Alejandro Colomar <alx@kernel.org>

libmisc/pwd2spwd.c

@@ -42,7 +42,7 @@ struct spwd *pwd_to_spwd (const struct passwd *pw)
 		 */
 		sp.sp_min = 0;
 		sp.sp_max = (10000L * DAY) / SCALE;
-		sp.sp_lstchg = (long) gettime () / SCALE;
+		sp.sp_lstchg = gettime () / SCALE;
 		if (0 == sp.sp_lstchg) {
 			/* Better disable aging than requiring a password
 			 * change */