Remove activityType and Id (#1179)

* Remove activityType and Id

* Fix tests

* Fix tests

server/src/database/migrations/20230811232332_remove_activity_commentable_type_and_commentable_id/migration.sql

@@ -0,0 +1,13 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `commentableId` on the `activity_targets` table. All the data in the column will be lost.
+  - You are about to drop the column `commentableType` on the `activity_targets` table. All the data in the column will be lost.
+
+*/
+-- AlterTable
+ALTER TABLE "activity_targets" DROP COLUMN "commentableId",
+DROP COLUMN "commentableType";
+
+-- DropEnum
+DROP TYPE "CommentableType";