[Event] Remove ability to disable an org's fronted transactions

When we originally launched fronted transactions, we kept around a switch to disable fronted transactions for a specific organization. That is no longer necessary and really has no good use case.

@Luke-Oldenburg has checked in Prod that we don't use this.

Let's remove this switch / logic from our codebase.

Search the Ruby codebase for the organization-specific switch and logic controlling whether fronted transactions can be disabled. Read the surrounding transaction and organization code, then run the relevant test suite; done means the unused disable path and its references are removed without breaking fronted transaction behavior.

Written by the indexing model from the issue text.