validations: drop superfluous return statements.

Returning true or false in a validation callback doesn't do anything, so
drop these superfluous return statements.

app/models/post_appeal.rb

@@ -75,18 +75,12 @@ class PostAppeal < ApplicationRecord
   def validate_creator_is_not_limited
     if appeal_count_for_creator >= Danbooru.config.max_appeals_per_day
       errors[:creator] << "can appeal at most #{Danbooru.config.max_appeals_per_day} post a day"
-      false
-    else
-      true
     end
   end
 
   def validate_post_is_inactive
     if resolved?
       errors[:post] << "is active"
-      false
-    else
-      true
     end
   end