Remove duplicate onroof/onground assignment for vertical moving plats

The onroof/onground attributes are used to determine if the player is
standing on a surface and is eligible to flip. Most notably, it is an
integer and not a boolean, and it starts at 2, giving the player 2
frames to edge-flip, i.e. they can still flip 2 frames after walking off
an edge.

However, these attributes are unnecessarily reassigned in
movingplatformfix() (which is the function that deals exclusively with
vertically-moving platforms; horizontal moving platforms get their own
hormovingplatformfix()). Whoever wrote this misunderstood what
onroof/onground meant; they thought that they were booleans, and so set
them to true, instead of the proper value of 2. This ends up setting
onroof/onground to 1 instead of 2, causing a discrepancy with vertical
moving platforms and the rest of the surfaces in the game.

The bigger mistake here is duplicating code that never needed to be
duplicated. The onroof/onground assignment in gamelogic() works
perfectly fine for vertical moving platforms. Indeed, after testing it
with libTAS, I can confirm that removing the duplicate assignments
restores being able to edge-flip off of moving platforms with 2 frames
of leeway, instead of only 1 frame. It also doesn't change how long it
takes for the onroof/onground to get set when the player is recognized
as standing on a vertically-moving platform, either.

And so, it's better to not duplicate this code, because when you
duplicate it you run the risk of making a mistake, as I just
demonstrated.

desktop_version/src/Entity.cpp

@@ -4473,13 +4473,11 @@ void entityclass::movingplatformfix( int t, int j )
                 {
                     entities[j].yp = entities[t].yp + entities[t].h;
                     entities[j].vy = 0;
-                    entities[j].onroof = true;
                 }
                 else
                 {
                     entities[j].yp = entities[t].yp - entities[j].h-entities[j].cy;
                     entities[j].vy = 0;
-                    entities[j].onground = true;
                 }
             }
             else