remove ping - it's not actually used anymore

backend/mediaprovider/jellyfin/jellyfinserver.go

@@ -12,7 +12,3 @@ type JellyfinServer struct {
 func (j *JellyfinServer) MediaProvider() mediaprovider.MediaProvider {
 	return newJellyfinMediaProvider(&j.Client)
 }
-
-func (j *JellyfinServer) Ping() bool {
-	return false // TODO: unimplemented
-}

backend/mediaprovider/mediaprovider.go

@@ -35,7 +35,6 @@ type Favorites struct {
 }
 
 type Server interface {
-	Ping() bool
 	Login(username, password string) error
 	MediaProvider() MediaProvider
 }