Remove code from old join community flows

[ilmotta]

Problem

After we implemented the new join community flow allowing users to select wallet accounts to share, we kept the old implementation behind the feature flag community-accounts-selection-enabled (always set to true in develop). This is an easy source of confusion.

Implementation

The new code is considered stable and has been QAed at the time of implementation and working well for a few months. Therefore, we want to remove all the old code.

Places where you can start (non-exhaustive list):

• Remove event :communities/request-to-join and other events using it.
• Remove old unit tests
• Remove Screen :community-requests-to-join
• Check namespace status-im.contexts.communities.actions.request-to-join.view
• Remove the flag community-accounts-selection-enabled?

Acceptance Criteria

Recommended to get the PR through QA, at least as a smoke check.