On non-MS-Windows, omit unnecessary polling functions

* src/keyboard.c (poll_for_input_1) [!CYGWIN && !DOS_NT]: Remove.
(input_polling_used) [!DOS_NT]: Remove.

src/keyboard.c

@@ -1871,6 +1871,7 @@ int poll_suppress_count;
 
 static struct atimer *poll_timer;
 
+#if defined CYGWIN || defined DOS_NT
 /* Poll for input, so that we catch a C-g if it comes in.  */
 void
 poll_for_input_1 (void)
@@ -1879,6 +1880,7 @@ poll_for_input_1 (void)
       && !waiting_for_input)
     gobble_input ();
 }
+#endif
 
 /* Timer callback function for poll_timer.  TIMER is equal to
    poll_timer.  */
@@ -1930,20 +1932,22 @@ start_polling (void)
 #endif
 }
 
+#ifdef DOS_NT
 /* True if we are using polling to handle input asynchronously.  */
 
 bool
 input_polling_used (void)
 {
-#ifdef POLL_FOR_INPUT
+# ifdef POLL_FOR_INPUT
   /* XXX This condition was (read_socket_hook && !interrupt_input),
      but read_socket_hook is not global anymore.  Let's pretend that
      it's always set.  */
   return !interrupt_input;
-#else
-  return 0;
-#endif
+# else
+  return false;
+# endif
 }
+#endif
 
 /* Turn off polling.  */