MM-31064: Simplify indentation (#16565)

* MM-31064: Simplify indentation

Reduce indentation where possible.

```release-note
NONE
```

Command ran to verify:
golangci-lint run --disable-all --enable golint --max-issues-per-linter=10000 --max-same-issues=100000 ./... | grep "block ends with a return state"

https://mattermost.atlassian.net/browse/MM-31064

* incorporate review comments

* enable golint for outdent rule

* fix remaining issues

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/channel.go

@@ -341,9 +341,8 @@ func (o *Channel) GetOtherUserIdForDM(userId string) string {
 func GetDMNameFromIds(userId1, userId2 string) string {
 	if userId1 > userId2 {
 		return userId2 + "__" + userId1
-	} else {
-		return userId1 + "__" + userId2
 	}
+	return userId1 + "__" + userId2
 }
 
 func GetGroupDisplayNameFromUsers(users []*User, truncate bool) string {