(main): Remove declaration of unused local, c.

src/logname.c

@@ -57,7 +57,6 @@ int
 main (int argc, char **argv)
 {
   register char *cp;
-  int c;
 
   initialize_main (&argc, &argv);
   program_name = argv[0];

src/printenv.c

@@ -78,7 +78,6 @@ main (int argc, char **argv)
   char **env;
   char *ep, *ap;
   int i;
-  int c;
   bool ok;
 
   initialize_main (&argc, &argv);

src/sleep.c

@@ -101,7 +101,6 @@ main (int argc, char **argv)
 {
   int i;
   double seconds = 0.0;
-  int c;
   bool ok = true;
 
   initialize_main (&argc, &argv);