Config: Removes setting viewers_can_edit (#101767)

Reapply "Authz: Removes setting `viewers_can_edit`" (#101528)

This reverts commit 5f6b00a72f.

pkg/api/accesscontrol.go

@@ -71,11 +71,6 @@ func (hs *HTTPServer) declareFixedRoles() error {
 		Grants: []string{string(org.RoleEditor)},
 	}
 
-	//nolint:staticcheck // ViewersCanEdit is deprecated but still used for backward compatibility
-	if hs.Cfg.ViewersCanEdit {
-		datasourcesExplorerRole.Grants = append(datasourcesExplorerRole.Grants, string(org.RoleViewer))
-	}
-
 	datasourcesReaderRole := ac.RoleRegistration{
 		Role: ac.RoleDTO{
 			Name:        "fixed:datasources:reader",