Remove further instances of st_diffs

db/migrate/limits_to_mysql.rb

@@ -2,19 +2,6 @@ class LimitsToMysql < ActiveRecord::Migration[4.2]
   def up
     return unless ActiveRecord::Base.configurations[Rails.env]['adapter'] =~ /^mysql/
 
-    # These columns were removed in 10.3, but this is called from two places:
-    # 1. A migration run after they were added, but before they were removed.
-    # 2. A rake task which can be run at any time.
-    #
-    # Because of item 2, we need these checks.
-    if column_exists?(:merge_request_diffs, :st_commits)
-      change_column :merge_request_diffs, :st_commits, :text, limit: 2147483647
-    end
-
-    if column_exists?(:merge_request_diffs, :st_diffs)
-      change_column :merge_request_diffs, :st_diffs, :text, limit: 2147483647
-    end
-
     change_column :snippets, :content, :text, limit: 2147483647
     change_column :notes, :st_diff, :text, limit: 2147483647
   end

lib/gitlab/import_export/import_export.yml

@@ -133,7 +133,6 @@ excluded_attributes:
     - :external_diff
     - :stored_externally
     - :external_diff_store
-    - :st_diffs
   merge_request_diff_files:
     - :diff
     - :external_diff_offset