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/system.go

@@ -184,9 +184,8 @@ func WarnMetricStatusFromJson(data io.Reader) *WarnMetricStatus {
 	var o WarnMetricStatus
 	if err := json.NewDecoder(data).Decode(&o); err != nil {
 		return nil
-	} else {
-		return &o
 	}
+	return &o
 }
 
 func MapWarnMetricStatusToJson(o map[string]*WarnMetricStatus) string {