remove beta label from final grade override feature option

This commit also clarifes functionality in the K-12
Specific Features feature option and also removes
the beta label.

CLOSES: GRADE-2379

Test plan:
- Open Account Settings
- Open Feature Options tab
- View beta label removed from final grade override

Change-Id: I595bddd5cd6ba4222ddd1b397f2370cb2b665426
Reviewed-on: https://gerrit.instructure.com/205501
Tested-by: Jenkins
Reviewed-by: Keith Garner <kgarner@instructure.com>
Product-Review: Keith Garner <kgarner@instructure.com>
QA-Review: Erin Hallmark <erin@instructure.com>

config/feature_flags/00_standard.yml

@@ -107,18 +107,15 @@ final_grades_override:
   applies_to: Course
   root_opt_in: true
   custom_transition_proc: final_grades_override_custom_transition_hook
-  beta: true
 k12:
   state: hidden
   display_name:
     features.k12: K-12 Specific Features
   description:
     k12_description: |-
-      Features, settings and styles that make more sense specifically in a K-12 environment. For now, this only
-      applies some style changes, but more K-12 specific things may be added in the future.
+      Update the icons in the Global Navigation Menu that make more sense specifically in a K-12 environment.
   applies_to: RootAccount
   root_opt_in: true
-  beta: true
 recurring_calendar_events:
   state: hidden
   display_name: Duplicating Calendar Events