deactivating a user leaves it in communities.

[airblag]

Description

I'm having a setup with mxisd, and synapse, using the rest-api to authenticate my users against my LDAP server.
When a user is removed from LDAP, I also wanna deactivate his/her access to Matrix too.
The user is leaving all rooms but staying in communities it was part of. I guess it would be more consequent to leave communities at the same time.

Steps to reproduce

• Create a user
• invite it to a community
• log with this user and join the community and a room
• with an admin token, deactivate his account :

curl -s -XPOST "https://mymatrixserver.net/_matrix/client/r0/admin/deactivate/%40testuser%3Amymatrixserver.net?access_token=$token" -d '{}'

• @testuser:mymatrixserver.net is then leaving all rooms it was in, and all tokens are revoked, but
  the user is staying in all communities it joined/was invited to.

I would expect that the user is also leaving communities when the account is deactivated.

Version information

• Homeserver: company internal synapse server

If not matrix.org:

• Version: 0.31.1-1 (from https://matrix.org/packages/debian stretch InRelease)
• Install method: package manager
• Platform: debian stretch lxd container (host is ubuntu 17.04), but I don't think it has any influence :)

[dklimpel]

Related to #11539

[clokep]

Communities/groups are being removed, see #11584.