Simplify issuable finder queries

We had `item_project_ids` to help make slow queries on the dashboard faster, but
this isn't necessary any more - the queries are plenty fast, and we forbid
searching the dashboard without filters.

app/controllers/concerns/issuable_collections.rb

@@ -95,12 +95,6 @@ module IssuableCollections
     elsif @group
       @filter_params[:group_id] = @group.id
       @filter_params[:include_subgroups] = true
-    else
-      # TODO: this filter ignore issues/mr created in public or
-      # internal repos where you are not a member. Enable this filter
-      # or improve current implementation to filter only issues you
-      # created or assigned or mentioned
-      # @filter_params[:authorized_only] = true
     end
 
     @filter_params.permit(finder_type.valid_params)

app/finders/issuable_finder.rb

@@ -159,10 +159,7 @@ class IssuableFinder
         finder_options = { include_subgroups: params[:include_subgroups], only_owned: true }
         GroupProjectsFinder.new(group: group, current_user: current_user, options: finder_options).execute
       else
-        opts = { current_user: current_user }
-        opts[:project_ids_relation] = item_project_ids(items) if items
-
-        ProjectsFinder.new(opts).execute
+        ProjectsFinder.new(current_user: current_user).execute
       end
 
     @projects = projects.with_feature_available_for_user(klass, current_user).reorder(nil)

app/finders/issues_finder.rb

@@ -136,8 +136,4 @@ class IssuesFinder < IssuableFinder
       items
     end
   end
-
-  def item_project_ids(items)
-    items&.reorder(nil)&.select(:project_id)
-  end
 end

app/finders/merge_requests_finder.rb

@@ -56,8 +56,4 @@ class MergeRequestsFinder < IssuableFinder
 
     items.where(target_branch: target_branch)
   end
-
-  def item_project_ids(items)
-    items&.reorder(nil)&.select(:target_project_id)
-  end
 end