remove anonymous moderated marking release flag

The flag was unused and can be removed safely.

flag=anonymous_moderated_marking

Test Plan:
- specs pass

Change-Id: I5bd379191889cba218e0c754509b2680a239f6d7
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/247635
Reviewed-by: Aaron Shafovaloff <ashafovaloff@instructure.com>
Reviewed-by: Syed Hussain <shussain@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Spencer Olson <solson@instructure.com>
Product-Review: Syed Hussain <shussain@instructure.com>

config/feature_flags/02_anonymous_moderated_marking.yml

@@ -1,16 +1,4 @@
 ---
-anonymous_moderated_marking:
-  state: hidden
-  display_name: Anonymous Moderated Marking
-  description: Anonymous Moderated Marking allows teachers to select moderators to
-    anonymously grade assignments. After which a moderator can select or supply a
-    custom grade.
-  applies_to: Account
-  root_opt_in: true
-  beta: true
-  environments:
-    production:
-      state: disabled
 anonymous_marking:
   state: allowed
   display_name: Anonymous Grading

spec/lib/data_fixup/backfill_moderation_graders_spec.rb

@@ -20,7 +20,6 @@ require 'spec_helper'
 describe DataFixup::BackfillModerationGraders do
   before(:once) do
     @root_account = account_model
-    @root_account.enable_feature!(:anonymous_moderated_marking)
     course_factory(account: @root_account)
     @student = User.create!
     @course.enroll_student(@student)