Removal of "cannot add members" after 10 minute mark

[WellFooled]

It seems that there were complaints in other languages about players Joining In Progress into games that were already won/lost.

This makes sense, but I think some adjustment is in order. I usually see the message right about the time the nodes at markets/temple/manor spawn, which means one team might be at 25 points. This is too early in the match to stop filling party slots.