Drop show_diff_preview_in_email column

Removes show_diff_previow_in_email column per our dropping column
process.

Changelog: changed

db/post_migrate/20220221214928_remove_show_diff_preview_in_email_column.rb

+# frozen_string_literal: true
+
+class RemoveShowDiffPreviewInEmailColumn < Gitlab::Database::Migration[1.0]
+  enable_lock_retries!
+
+  def up
+    remove_column :project_settings, :show_diff_preview_in_email, :boolean
+  end
+
+  def down
+    add_column :project_settings, :show_diff_preview_in_email, :boolean, default: true, null: false
+  end
+end

db/schema_migrations/20220221214928

+8c9936d1c0f728c2b40dca536f9edb40f4af94a274ccf1dbec984f218710f695
\ No newline at end of file

db/structure.sql

@@ -18766,7 +18766,6 @@ CREATE TABLE project_settings (
     merge_commit_template text,
     has_shimo boolean DEFAULT false NOT NULL,
     squash_commit_template text,
-    show_diff_preview_in_email boolean DEFAULT true NOT NULL,
     legacy_open_source_license_available boolean DEFAULT true NOT NULL,
     CONSTRAINT check_3a03e7557a CHECK ((char_length(previous_default_branch) <= 4096)),
     CONSTRAINT check_b09644994b CHECK ((char_length(squash_commit_template) <= 500)),