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/ttytype.c

@@ -43,7 +43,7 @@ void ttytype (const char *line)
 		perror (typefile);
 		return;
 	}
-	while (fgets (buf, (int) sizeof buf, fp) == buf) {
+	while (fgets (buf, sizeof buf, fp) == buf) {
 		if (buf[0] == '#') {
 			continue;
 		}