Pawn move repetition

[Starlight-30036225]

With the changes I made to the validate move function, the code for pawn moves needs to be updates.

Currently, it calls validatemove for its return value, then adds a move if that is true. This is now redundant as validate move handles adding a successful move to the list, so i can change this:

[Starlight-30036225]

Only a slight change, but these moves will now no longer be added to the list twice.