chore: remove conditional frontend routing

[justynoh]

Problem

We need to remove the ability for users to go back to using angular.

Closes #6122

Solution

This PR removes all references to incremental roll out env vars and logic for react migration. All users will be on react, and angular will never be served again.

Much is still left to be done (see below).

Breaking Changes

• No - this PR is backwards compatible

Tests

For all of these tests, perform them 3 ways: 1) cleared cookies, 2) with v2-(admin|respondent)-ui=react, 3) with v2-(admin|respondent)-ui=angular

• Ensure that the React landing page can be accessed.
  • The landing page loads
  • Statistics are loaded correctly
• Admin features
  • Workspace should be accessible, forms should load correctly
  • Admin banner should not be visible
  • Feedback icon should not be visible
• Public form
  • Form should load correctly with no errors
  • Switch env banner at the bottom of the page should not load.
• /environment does not work anymore
  • Going to /environment/react does not add the react cookie.
  • Going to /environment/angular does not add the angular cookie.

Deploy notes

• Remove the following env vars:
  • REACT_MIGRATION_RESP_ROLLOUT_EMAIL
  • REACT_MIGRATION_RESP_ROLLOUT_STORAGE
  • REACT_MIGRATION_ADMIN_ROLLOUT
  • REACT_MIGRATION_RESP_COOKIE_NAME
  • REACT_MIGRATION_ADMIN_COOKIE_NAME_OLD
  • REACT_MIGRATION_ADMIN_COOKIE_NAME
  • REACT_MIGRATION_QA_COOKIE_NAME
  • REACT_MIGRATION_ANGULAR_END_DATE
  • REACT_MIGRATION_REMOVE_INFOBOX_THRESHOLD_ADMIN
  • REACT_MIGRATION_REMOVE_INFOBOX_THRESHOLD_RESPONDENT
  • REACT_SWITCH_ENV_FEEDBACK_FORM_ID_ADMIN
  • REACT_SWITCH_ENV_FEEDBACK_FORM_ID_RESPONDENT
• Since the angular /#!/terms page is now no more accessible via routing, ensure that the Load Balancer target group health check for prod is updated to api/v3/analytics/statistics with success codes 200,304 prior to deployment.

Notes

To do:

• Delete angular code
• Delete old deprecated routes
• remove useFetchForSubmissions
• migrate react banners to using non-react-suffixed env vars
• Delete GA Tracking ID env var (only used in Angular) - GA Tracking ID (Angular) cleanup #4786
• Delete rollout announcement Rollout announcement to be repurposed for new features
• Delete e2e tests

[wanlingt]

waaaaa

[wanlingt]

lgtm other than a few nits! MOMENTOUS PR

[wanlingt]

I've also added another TODO to the list (#4786). Relatedly, was there a conclusion we reached regarding useFetchForSubmissions?

@kennethchangOPENGOV says we're meeting with the user experiencing lagginess on React next Tues morn, we can aim to merge this in after that!

[justynoh]

Tagging @timotheeg for decision re: useFetchForSubmissions

[justynoh]

Update: we'll keep useFetchForSubmissions for a while longer.