import: Remove deprecated WikiRevision::$importer property

This property was introduced since 1.17 and was unused, then following
the deprecation policy, it was deprecated in 1.29. Removing this now
as it's been long enough and has been for several MW versions. Also,
updated release notes to mention this removal.

Change-Id: Ib6353dd37079bcfe7cd15600e8af1f67b245f4a3

RELEASE-NOTES-1.33

@@ -246,6 +246,7 @@ because of Phabricator reports.
   Use require( 'mediawiki.libs.jpegmeta' ) instead.
 * The mw.user.stickyRandomId() method, deprecated in 1.32, was removed.
   Use mw.user.getPageviewToken() instead.
+* Removed deprecated class property WikiRevision::$importer.
 
 === Deprecations in 1.33 ===
 * The configuration option $wgUseESI has been deprecated, and is expected

includes/import/WikiRevision.php

@@ -36,13 +36,6 @@ use MediaWiki\MediaWikiServices;
  */
 class WikiRevision implements ImportableUploadRevision, ImportableOldRevision {
 
-	/**
-	 * @since 1.17
-	 * @deprecated in 1.29. Unused.
-	 * @note Introduced in 9b3128eb2b654761f21fd4ca1d5a1a4b796dc912, unused there, unused now.
-	 */
-	public $importer = null;
-
 	/**
 	 * @since 1.2
 	 * @var Title