docs: delete_chat(): Don't lie that messages aren't deleted from server

[iequidoo]

Messages are actually deleted from the server. I've checked this in Desktop.

See ChatId::delete_ex():

"UPDATE imap SET target=? WHERE rfc724_mid IN (SELECT rfc724_mid FROM msgs WHERE chat_id=?)",
(delete_msgs_target, self,),

[r10s]

thanks a lot for taking care!

however, we should start speaking also in core more about "relay" and not "server" - it makes a difference over time. so i'd change "server" to "relay" here for new things we document

[iequidoo]

Decided not to change "server" to "relay" yet. Maybe better to make such a replacement in all places in a separate PR to avoid having mixed wording

[link2xt]

We also have some inconsistency like "account" <-> "profile" between core and UIs. If it is still called "transport" in SQL and APIs such as events then maybe better keep it this way in the core.