posts: remove rating, note, and status locks.

Remove the ability for users to lock ratings, note, and post statuses.

Historically the majority of locked posts were from 10+ years ago when
certain users habitually locked ratings and notes on every post they
touched for no reason. Nowadays most posts have been unlocked. Only a
handful of locked posts are left, none of which deserve to be locked.

The is_rating_locked, is_note_locked, and is_status_locked columns still
exist in the database, but aren't used.

app/models/post_flag.rb

@@ -99,7 +99,6 @@ class PostFlag < ApplicationRecord
   def validate_post
     errors.add(:post, "is pending and cannot be flagged") if post.is_pending? && !is_deletion
     errors.add(:post, "is deleted and cannot be flagged") if post.is_deleted? && !is_deletion
-    errors.add(:post, "is locked and cannot be flagged") if post.is_status_locked?
 
     flag = post.flags.in_cooldown.last
     if !is_deletion && flag.present?