Chore: Remove unused Go code (#28852)

* Chore: Remove more unused Go code

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/api/dtos/index.go

@@ -23,11 +23,6 @@ type IndexViewData struct {
 	Sentry                  *setting.Sentry
 }
 
-type PluginCss struct {
-	Light string `json:"light"`
-	Dark  string `json:"dark"`
-}
-
 const (
 	// These weights may be used by an extension to reliably place
 	// itself in relation to a particular item in the menu. The weights