Remove tour to drop problematic dependency

* Drop problematic dependency `shepherd.js`
* Keep the database column to avoid a problematic database migration
* Keep the API endpoint to set the tour progress to avoid a breaking API
  change
* Note that we might want to repurpose the database column and API in the
  future to show a simple help notification for new users
* Add a very small test for the feature API so it is still covered after
  removing the UI test of the feature tour
* Remove all UI code related to the tour
* See https://progress.opensuse.org/issues/163004 for further reasoning

assets/assetpack.def

@@ -141,7 +141,6 @@
 < javascripts/filter_form.js
 < javascripts/comments.js
 < javascripts/keyevent.js
-< javascripts/feature.js
 < javascripts/fullscreen.js
 < javascripts/obs_rsync.js
 < javascripts/parent_group_overview.js
@@ -150,7 +149,6 @@
 < ../node_modules/chosen-js/chosen.jquery.js
 < ../node_modules/jquery-ujs/src/rails.js
 < javascripts/disable_animations.js [mode==test]
-< ../node_modules/shepherd.js/dist/js/shepherd.min.js
 
 ! anser.js
 < javascripts/anser-import.js

assets/stylesheets/openqa.scss

@@ -23,4 +23,3 @@ dummy { font-size: 42px; }
 @import "comments.scss";
 @import "overview.scss";
 @import "parent_group_overview.scss";
-@import "shepherd.scss";

lib/OpenQA/WebAPI/Controller/API/V1/Feature.pm

@@ -21,7 +21,7 @@ Implements feature API.
 
 =item informed()
 
-Post integer value to save feature tour progress of current user in the database
+Post integer value to save feature version of current user in the database
 
 =back