Various code cleanup (#1782)

* Remove duplicate in_chosen_languages definition

* Use `DEFAULT_FIELDS_SIZE` instead of `MAX_FIELDS` to reduce code differences with upstream

* Remove duplicate annotation

* Fix incorrect cross-flavor imports

* Remove deprecated `hide_network` setting (replaced by account column)

* Remove unused KeywordMutesHelper

* Remove trailing spaces

* Remove commit_hash from InstancePresenter, as it has been unused since mid-2017

app/presenters/instance_presenter.rb

@@ -44,15 +44,6 @@ class InstancePresenter
     Mastodon::Version
   end
 
-  def commit_hash
-    current_release_file = Pathname.new('CURRENT_RELEASE').expand_path
-    if current_release_file.file?
-      IO.read(current_release_file).strip!
-    else
-      ''
-    end
-  end
-
   def source_url
     Mastodon::Version.source_url
   end