chore: make all the deprecated feature flag reclaimable (#13646)

## Docs

https://www.notion.so/chatwoot/Redeeming-a-depreciated-feature-flag-313a5f274c9280f381cdd811eab42019?source=copy_link

## Description
Marks 8 unused feature flags as deprecated: true in features.yml,
freeing their bit slots for future reuse.
Removes dead code references from JS constants, help URLs, and
enterprise billing config.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

- Simulated the "claim a slot" workflow 

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

enterprise/app/services/enterprise/billing/handle_stripe_event_service.rb

@@ -11,7 +11,6 @@ class Enterprise::Billing::HandleStripeEventService
     help_center
     campaigns
     team_management
-    channel_twitter
     channel_facebook
     channel_email
     channel_instagram

enterprise/config/premium_features.yml

@@ -1,7 +1,6 @@
 # List of the premium features in EE edition
 - disable_branding
 - audit_logs
-- response_bot
 - sla
 - custom_roles
 - captain_integration