Remove matrix-bridge-mx-* roles which have alternative

[luixxiul]

Is your feature request related to a problem? Please describe.

@spantaleev reports at https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/CHANGELOG.md#backward-compatibility-break-synapse-now-defaults-to-enabling-authenticated-media:

Old and unmaintained bridges (like all mx-puppet bridges, etc.) do not support authenticated media. Other software may be similarly affected. If you experience issues with some Matrix-related software, you may wish to disable authenticated media and contact the software maintainers to let them know.

I assume it would be acceptable to remove these roles if fixing incompatibilities require him (or other persons) so much work, especially of mx bridges which there are alternative for, such as:

• matrix-bridge-mx-puppet-discord (alternatives: matrix-bridge-appservice-discord, matrix-bridge-mautrix-discord)
• matrix-bridge-mx-puppet-instagram (alternative: matrix-bridge-mautrix-meta-instagram)
• matrix-bridge-mx-puppet-slack (alternative: matrix-bridge-mautrix-slack. Note: matrix-bridge-appservice-slack is available only if classic app has been created)
• matrix-bridge-mx-puppet-twitter (alternative: matrix-bridge-mautrix-twitter)

There is also a report that the current documentation for mx-puppet-steam is not correct: #1371 (although it is not sure whether the role itself has become outdated or not)

As the role for Google Hangouts is scheduled to be removed from the playbook (see here), I assume the same kind of plan can be applied to the mx bridges removal. Besides, if the issues will be fixed by the upstream project, it should be relatively easy to re-implement the bridges by reverting the change.

Describe the solution you'd like

Describe alternatives you've considered

Additional context
(This suggestion is per communication with Slavi)