Disable pressing R in No Death Mode

All that pressing R does in No Death Mode is end your run. As a result,
it'll only be pressed by accident, so it's better to just disable it
instead.

It's not even useful to quick-restart, because it's faster to quit and
go through the menu again than it is to wait through the Game Over
screen.

Additionally, I removed the `game.deathseq<=0` conditional because it's
unnecessary due to the if-statement already being inside a
`game.deathseq == -1` conditional.

desktop_version/src/Input.cpp

@@ -1899,7 +1899,7 @@ void gameinput()
                     }
                 }
 
-                if (key.keymap[SDLK_r] && game.deathseq<=0)// && map.custommode) //Have fun glitchrunners!
+                if (key.keymap[SDLK_r] && !game.nodeathmode)// && map.custommode) //Have fun glitchrunners!
                 {
                     game.deathseq = 30;
                 }