Stop nerfing BP progression

@BaldWraithSimp  It's probably a deliberate mechanism to prevent arenas from dying out, since it's been added as a third permanent mode. Which is particularly unfair as although I did find my playtime in arenas quite fun, it did feel like a beta test still.

I imagine it's still possible to complete the BP without doing the challenges for Arena....it's just be much closer to the deadline for us more casual players.