Macaron cleanup (#37795)

* simplify some dependency injection in macaron
* remove unused internal server error handler from macaron
* remove internal server error handler from the router
* remove unused combo router api
* remove unused parts of the macaron router

pkg/api/http_server.go

@@ -136,8 +136,6 @@ func ProvideHTTPServer(opts ServerOptions, cfg *setting.Cfg, routeRegister routi
 	socialService social.Service, oauthTokenService oauthtoken.OAuthTokenService) (*HTTPServer, error) {
 	macaron.Env = cfg.Env
 	m := macaron.New()
-	// automatically set HEAD for every GET
-	m.SetAutoHead(true)
 
 	hs := &HTTPServer{
 		Cfg:                    cfg,