Remove dead code guarded with "#if 0 … #endif" (#2338)

This code has been neutralized for many years now and served no purpose
other than cluttering up the code. We obviously don't need it and it's
out of date anyway.

If there's ever any reason to restore (parts of) it, we have git for
that. But we don't need to keep commented out code around.

i3-input/main.c

@@ -216,10 +216,6 @@ static void finish_input() {
 
     free(full);
 
-#if 0
-    free(command);
-    return 1;
-#endif
     exit(0);
 }