FeatureFlags: Revert managing feature flags outside of settings.Cfg (#44382)

* Revert "FeatureToggles: register all enterprise feature toggles (#44336)"

This reverts commit f53b3fb007.

* Revert "FeatureFlags: manage feature flags outside of settings.Cfg (#43692)"

This reverts commit f94c0decbd.

pkg/setting/setting_unified_alerting_test.go

@@ -143,7 +143,6 @@ func TestUnifiedAlertingSettings(t *testing.T) {
 		t.Run(tc.desc, func(t *testing.T) {
 			f := ini.Empty()
 			cfg := NewCfg()
-			cfg.IsFeatureToggleEnabled = func(key string) bool { return false }
 			unifiedAlertingSec, err := f.NewSection("unified_alerting")
 			require.NoError(t, err)
 			for k, v := range tc.unifiedAlertingOptions {