docs: @DELETE
      @Path("{token: .*}")
      public Response unregisterInstallations(
              @PathParam("token") String token,
              @Context HttpServletRequest request) {
  
          // find the matching variation:
          final Variant variant = loadVariantWhenAuthorized(request);
          if (variant == null) {
              return create401Response(request);
          }
  
          // look up all installations (with same token) for the given variant:
          Installation installation =
                  clientInstallationService.findInstallationForVariantByDeviceToken(variant.getVariantID(), token);
  
          if (installation == null) {
              return appendAllowOriginHeader(Response.status(Status.NOT_FOUND), request);
          }
  
          logger.info("Deleting metadata Installation");
          // remove
          clientInstallationService.removeInstallation(installation);
  
          return appendAllowOriginHeader(Response.noContent(), request);
      }