Remove some of our changes

[tkeemon]

These two changes:

• https://github.com/appsembler/configuration/blob/a41fb7953898829ac82a29dd747c7b7db7a67aa8/playbooks/roles/edxapp/defaults/main.yml#L18-L21
• https://github.com/appsembler/configuration/blob/a41fb7953898829ac82a29dd747c7b7db7a67aa8/playbooks/roles/edxapp/defaults/main.yml#L806

can be removed from our version of the fork if we do the following in each customer's server-vars.yml file:

---
EDXAPP_APPSEMBLER_FEATURES: 
  FEATURE_1: value
  FEATURE_2: value

EDXAPP_ENV_EXTRA:
  APPSEMBLER_FEATURES: "{{ EDXAPP_APPSEMBLER_FEATURES }}"

[natea]

@tkeemon agreed that let's try to remove as many customizations from the playbooks as possible, and encapsulate them in server-vars.yml so they're all in one place.

[OmarIthawi]

Thanks TJ for the note. It's 2021 but not too late to address this tech debt. My tentative plan is to remove APPSEMBLER_FEATURES['ENABLE_XYZ'] in favor of settings.FEATUES['TAHOE_ENABLE_XYZ'].