Remove active games when challenge canceled

[MarkZH]

Fixes #1166

Type of pull request:

• Bug fix
• Feature
• Other

Description:

If a challenge is accepted by a bot, but the challenge is canceled before the game starts, then the game ID remains in the active_games set and will never be removed. This effectively reduces the number of simultaneous games a bot can play by one each time it happens. This change removes the game ID from active_games when a challenge is canceled.

Related Issues:

Fixes #1166

Checklist:

• I have read and followed the contribution guidelines.
• I have added necessary documentation (if applicable).
• The changes pass all existing tests.

Screenshots/logs (if applicable):

[AttackingOrDefending]

If we get more bugs with active_games it might be worth periodically overwriting active games with the games we get from li.get_ongoing_games() just like we do at startup as a fail-safe.