posts: remove unused exception classes.

app/logical/post_query_builder.rb

@@ -947,8 +947,6 @@ class PostQueryBuilder
 
       set_cached_count(count) if count.present?
       count
-    rescue Post::SearchError
-      nil
     end
 
     def set_cached_count(count)

app/models/post.rb

@@ -1,10 +1,6 @@
 class Post < ApplicationRecord
-  class ApprovalError < StandardError; end
-  class DisapprovalError < StandardError; end
   class RevertError < StandardError; end
-  class SearchError < StandardError; end
   class DeletionError < StandardError; end
-  class TimeoutError < StandardError; end
 
   # Tags to copy when copying notes.
   NOTE_COPY_TAGS = %w[translated partially_translated check_translation translation_request reverse_translation

app/models/user.rb

@@ -1,5 +1,4 @@
 class User < ApplicationRecord
-  class Error < StandardError; end
   class PrivilegeError < StandardError; end
 
   module Levels