Alerting: Remove legacy alerting (#83671)

Removes legacy alerting, so long and thanks for all the fish! 🐟

---------

Co-authored-by: Matthew Jacobson <matthew.jacobson@grafana.com>
Co-authored-by: Sonia Aguilar <soniaAguilarPeiron@users.noreply.github.com>
Co-authored-by: Armand Grillet <armandgrillet@users.noreply.github.com>
Co-authored-by: William Wernert <rwwiv@users.noreply.github.com>
Co-authored-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>

pkg/api/frontendsettings.go

@@ -178,9 +178,6 @@ func (hs *HTTPServer) getFrontendSettings(c *contextmodel.ReqContext) (*dtos.Fro
 		LdapEnabled:                         hs.Cfg.LDAPAuthEnabled,
 		JwtHeaderName:                       hs.Cfg.JWTAuth.HeaderName,
 		JwtUrlLogin:                         hs.Cfg.JWTAuth.URLLogin,
-		AlertingErrorOrTimeout:              hs.Cfg.AlertingErrorOrTimeout,
-		AlertingNoDataOrNullValues:          hs.Cfg.AlertingNoDataOrNullValues,
-		AlertingMinInterval:                 hs.Cfg.AlertingMinInterval,
 		LiveEnabled:                         hs.Cfg.LiveMaxConnections != 0,
 		AutoAssignOrg:                       hs.Cfg.AutoAssignOrg,
 		VerifyEmailEnabled:                  hs.Cfg.VerifyEmailEnabled,
@@ -312,10 +309,6 @@ func (hs *HTTPServer) getFrontendSettings(c *contextmodel.ReqContext) (*dtos.Fro
 		frontendSettings.UnifiedAlertingEnabled = *hs.Cfg.UnifiedAlerting.Enabled
 	}
 
-	if hs.Cfg.AlertingEnabled != nil {
-		frontendSettings.AlertingEnabled = *(hs.Cfg.AlertingEnabled)
-	}
-
 	// It returns false if the provider is not enabled or the skip org role sync is false.
 	parseSkipOrgRoleSyncEnabled := func(info *social.OAuthInfo) bool {
 		if info == nil {