Lower cavalry melee attack range again.

D3482/rP24802 raised the melee attack range to 6 to compensate for movement over a turn with 500ms MP turns.
Following D3275/rP25001, this is no longer necessary. Revert to 4 (half the footprint length + 1 & their capture range).

Patch by: Nescio

Reviewed By: wraitii

Differential Revision: https://code.wildfiregames.com/D3673