-Removed unused values
-Added mine sound effect when select drill 2. Since it was missing, I also added it to the iron drill 2. Since iron drill 1 and 3 had it, I assume it was a simple mistake from the dev.

Several changes to bring the drills closer to the vanilla drills :
-Changed construction price of drill II and III
-Changed output efficiency of all drills (better in all cases)
-Reduced slope for building (it was changed on the iron drills, so I did the same)

Note that they will be slightly damaged when you play a game after update this specific patch for this mod. They'll be repaired automatically by an engineer if you have one in auto job. Once repaired they'll reach the new efficiency. This is because the building HP is calculated by the resources needed to build it, and the amount have slightly changed.

-Changed the research needed to match the new iron drill tree.