Clear miner predictions when it's deregistered

[ultrashiny]

check_hotkeys method in bettensor_validator.py detects changes in the hotkey list and clears scores for miners when they’re deregistered. However, reset_miner method in ScoringSystem doesn’t remove stored prediction data in the database for deregistered miners/hotkeys, which means this data persists.

This might affect a hotkey's score if it gets registered again. I recommend making an update to handle this:

• Either remove all database records related to a miner when it’s deregistered,
• Or add a new column in the predictions table to indicate if the data is from a currently active miner or a deregistered one.

[ultrashiny]

i might be wrong and please correct me if i'm mistaken

[ultrashiny]

https://github.com/Bettensor/bettensor/commit/e2766149434b2ac5b2d61ca4091e8eea6e4a0a85 i think, your new commit fixes this issue, @geardici what do you think?