Remove Beta Variables and Messaging

**User STory**
As a system, once launched to all institutions in production I no longer require an institution beta flag, student beta flag, or a full-time allowed flag. The system will be accepting both ft & pt applications for all students at this point and there will no longer be a split between systems.

**Acceptance Criteria**
- [ ] Remove institution beta, student beta and fulltime allowed environment variables (default should be fulltime allowed = true and no conditions on full-time)
- [ ] Cleanup the code to remove interactions with those variables

No files or tests are named. Search the repository for the institution beta, student beta, and full-time allowed environment variables and trace their usages before checking related configuration and tests. Done means those variables and their conditional interactions are removed, with full-time applications allowed by default and verification passing.

Written by the indexing model from the issue text.