dev191 - kind of remove DIV_ALWAYS_SET_VOLUME

it's useless crap I put during the Defle compat days
it serves nearly no purpose nowadays

also why is it a command?

src/engine/platform/arcade.cpp

@@ -783,9 +783,6 @@ int DivPlatformArcade::dispatch(DivCommand c) {
     case DIV_CMD_MACRO_ON:
       chan[c.chan].std.mask(c.value,false);
       break;
-    case DIV_ALWAYS_SET_VOLUME:
-      return 0;
-      break;
     case DIV_CMD_GET_VOLMAX:
       return 127;
       break;