FEATURE: Promote bookmarks with reminders to core functionality (#9369)

The main thrust of this PR is to take all the conditional checks based on the `enable_bookmarks_with_reminders` away and only keep the code from the `true` path, making bookmarks with reminders the core bookmarks feature. There is also a migration to create `Bookmark` records out of `PostAction` bookmarks for a site.

### Summary

* Remove logic based on whether enable_bookmarks_with_reminders is true. This site setting is now obsolete, the old bookmark functionality is being removed. Retain the setting and set the value to `true` in a migration.
* Use the code from the rake task to create a database migration that creates bookmarks from post actions.
* Change the bookmark report to read from the new table.
* Get rid of old endpoints for bookmarks
* Link to the new bookmarks list from the user summary page

test/javascripts/fixtures/user_fixtures.js

@@ -397,6 +397,34 @@ export default {
       featured_user_badge_ids: [5870, 40673, 5868]
     }
   },
+  "/u/eviltrout/bookmarks.json": {
+    user_bookmark_list: {
+      bookmarks: [
+        {
+          excerpt: "Here this is my new topic where I yell.",
+          tags: [],
+          id: 576,
+          created_at: "2020-04-07T05:30:40.446Z",
+          topic_id: 119,
+          linked_post_number: 1,
+          post_id: 281,
+          name: "test",
+          reminder_at: null,
+          title: "Yelling topic title :/",
+          deleted: false,
+          hidden: false,
+          category_id: 1,
+          closed: false,
+          archived: false,
+          archetype: "regular",
+          highest_post_number: 5,
+          bumped_at: "2020-04-06T05:20:00.172Z",
+          slug: "yelling-topic-title",
+          username: "someguy"
+        }
+      ]
+    }
+  },
   "/user_actions.json": {
     user_actions: [
       {