Avoid disabling deck validation with ALL_CARDS_AVAILABLE

[willroberts]

Summary

Describe your changes here. Remove any inapplicable sections.

App changes (app/, etc.):

• Replaces ALL_CARDS_AVAILABLE flag usage with DISABLE_DECK_VALIDATION flag in deck validation code

Server changes (config/, server/, worker/, etc.):

• Adds DISABLE_DECK_VALIDATION flag
• Removes unused PayPal/Mailchimp flags

Testing

Have you have tested your changes in the following scenarios?
Feel free to check off scenarios which don't apply.

• Starting backend services locally with docker compose up succeeds.
• I am able to create a new user and log in locally.
• I am able to complete a practice game locally.
• I am able to complete a purchase of Orbs, etc.