fix subtensor methods for async

[thewhaleking]

Fixes AsyncSubtensor and Subtensor methods:

• removes get_total_stake_for_coldkey, get_total_stake_for_coldkeys, get_total_stake_for_hotkey, get_total_stake_for_hotkeys
• fixes logic of get_hotkey_owner
• updates return type hint of get_subnet_burn_cost
• get_transfer_fee only accepts Balance type for value arg
• bonds doesn't return the None values in the map