Drop the account of the previous behaviour when attaching a shared chat

The paragraph says which kinds of access let you attach a conversation, which is what a reader needs. What used to happen instead is not their problem.

Author: Classic298

docs/features/chat-conversations/chat-features/chatshare.md

@@ -99,8 +99,7 @@ A chat that belongs to someone else is shown under its author: their name and pr
 
 #### Using a Shared Chat as Context
 
-Read access to a chat also lets you attach that conversation to a chat of your own, so a model can work from it. This covers a share granted to you by name, one granted to a group you belong to, one set to **Public** and a chat sitting in a [folder shared with you](/features/chat-conversations/chat-features/conversation-organization#sharing-folders). Previously only the chat's owner and admins got anything back: for everyone else the attachment was accepted and then contributed nothing, with no error to say so.
-
+Read access to a chat also lets you attach that conversation to a chat of your own, so a model can work from it. This covers a share granted to you by name, one granted to a group you belong to, one set to **Public** and a chat sitting in a [folder shared with you](/features/chat-conversations/chat-features/conversation-organization#sharing-folders).
 The model receives the conversation as it stands now, so messages added since the link was generated are included even though the link itself still serves the older snapshot. Only the branch the conversation is currently following is passed along. The text goes in verbatim, with no chunking and no vector search.
 
 ### Updating Shared Chats