MM-22051: Remove FromJson part 2 (#17981)

```release-note
Removed the following functions:
ChannelsWithCountFromJson
ChannelFromJson
ChannelPatchFromJson
ChannelModerationsFromJson
ChannelModerationsPatchFromJson
ChannelMemberCountsByGroupFromJson
ChannelCountsFromJson
ChannelDataFromJson
ChannelListFromJson
ChannelSliceFromJson
ChannelListWithTeamDataFromJson
ChannelMembersFromJson
ChannelUnreadFromJson
ChannelUnreadAtFromJson
ChannelMemberFromJson
ChannelSearchFromJson
SidebarCategoryFromJson
SidebarCategoriesFromJson
OrderedSidebarCategoriesFromJson
```

https://mattermost.atlassian.net/browse/MM-22051

model/channel.go

@@ -180,42 +180,6 @@ func (o *ChannelsWithCount) ToJson() []byte {
 	return b
 }
 
-func ChannelsWithCountFromJson(data io.Reader) *ChannelsWithCount {
-	var o *ChannelsWithCount
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
-func ChannelFromJson(data io.Reader) *Channel {
-	var o *Channel
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
-func ChannelPatchFromJson(data io.Reader) *ChannelPatch {
-	var o *ChannelPatch
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
-func ChannelModerationsFromJson(data io.Reader) []*ChannelModeration {
-	var o []*ChannelModeration
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
-func ChannelModerationsPatchFromJson(data io.Reader) []*ChannelModerationPatch {
-	var o []*ChannelModerationPatch
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
-func ChannelMemberCountsByGroupFromJson(data io.Reader) []*ChannelMemberCountByGroup {
-	var o []*ChannelMemberCountByGroup
-	json.NewDecoder(data).Decode(&o)
-	return o
-}
-
 func (o *Channel) Etag() string {
 	return Etag(o.Id, o.UpdateAt)
 }