Remove columns that were used for terraform state replication

- Remove indexes on the replication verification columns
- Removed constraint for verification failure text
- Removed columns that were ignored in 13.5

Relates to https://gitlab.com/gitlab-org/gitlab/issues/258262

changelogs/unreleased/alexives-258262-remove_columns_for_tf_state_validation.yml

+---
+title: Remove columns no longer used for replicating terraform state
+merge_request: 46742
+author:
+type: other

db/post_migrate/20201103013242_remove_terraform_state_verification_columns.rb

+# frozen_string_literal: true
+
+class RemoveTerraformStateVerificationColumns < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    transaction do
+      remove_column :terraform_states, :verification_retry_at, :datetime_with_timezone
+      remove_column :terraform_states, :verified_at, :datetime_with_timezone
+      remove_column :terraform_states, :verification_retry_count, :integer, limit: 2
+      remove_column :terraform_states, :verification_checksum, :binary, using: 'verification_checksum::bytea'
+      remove_column :terraform_states, :verification_failure, :text
+    end
+  end
+
+  def down
+    add_column(:terraform_states, :verification_retry_at, :datetime_with_timezone) unless column_exists?(:terraform_states, :verification_retry_at)
+    add_column(:terraform_states, :verified_at, :datetime_with_timezone) unless column_exists?(:terraform_states, :verified_at)
+    add_column(:terraform_states, :verification_retry_count, :integer, limit: 2) unless column_exists?(:terraform_states, :verification_retry_count)
+    add_column(:terraform_states, :verification_checksum, :binary, using: 'verification_checksum::bytea') unless column_exists?(:terraform_states, :verification_checksum)
+    add_column(:terraform_states, :verification_failure, :text) unless column_exists?(:terraform_states, :verification_failure)
+
+    add_text_limit :terraform_states, :verification_failure, 255
+  end
+end

db/schema_migrations/20201103013242

+8a30cf20f71e0cb198caf6f77a19e4da55b83eb38bdb5888cd2674373d94cede
\ No newline at end of file

db/structure.sql

@@ -16600,13 +16600,7 @@ CREATE TABLE terraform_states (
     locked_by_user_id bigint,
     uuid character varying(32) NOT NULL,
     name character varying(255),
-    verification_retry_at timestamp with time zone,
-    verified_at timestamp with time zone,
-    verification_retry_count smallint,
-    verification_checksum bytea,
-    verification_failure text,
-    versioning_enabled boolean DEFAULT false NOT NULL,
-    CONSTRAINT check_21a47163ea CHECK ((char_length(verification_failure) <= 255))
+    versioning_enabled boolean DEFAULT false NOT NULL
 );
 
 CREATE SEQUENCE terraform_states_id_seq