Revert " #4755 Combining consecutive user join/leave system messages to single message and few other changes." (#7072)

* Revert "PLT-6603: Don't return all posts on invalid query. (#7061)"

This reverts commit 25a2013890.

* Revert " #4755 Combining consecutive user join/leave system messages to single message and few other changes. (#5945)"

This reverts commit 8a91235fb3.

model/post.go

@@ -205,15 +205,6 @@ func (o *Post) IsSystemMessage() bool {
 	return len(o.Type) >= len(POST_SYSTEM_MESSAGE_PREFIX) && o.Type[:len(POST_SYSTEM_MESSAGE_PREFIX)] == POST_SYSTEM_MESSAGE_PREFIX
 }
 
-func (o *Post) IsUserActivitySystemMessage() bool {
-	return o.Type == POST_JOIN_LEAVE ||
-		o.Type == POST_JOIN_CHANNEL ||
-		o.Type == POST_LEAVE_CHANNEL ||
-		o.Type == POST_ADD_REMOVE ||
-		o.Type == POST_ADD_TO_CHANNEL ||
-		o.Type == POST_REMOVE_FROM_CHANNEL
-}
-
 func (p *Post) Patch(patch *PostPatch) {
 	if patch.IsPinned != nil {
 		p.IsPinned = *patch.IsPinned