skins: Remove deprecated SkinCopyrightFooter $forContent param

The $forContent parameter was deprecated six years ago and looks
like nothing else is using it (verified via codeseach.wmflabs.org)

Change-Id: I7c6093a083845a40b82e39c91006a5a0b223eab6

RELEASE-NOTES-1.35

@@ -202,6 +202,7 @@ because of Phabricator reports.
 * Skin::makeI18nUrl() and makeNSUrl() have been deprecated, no longer used.
 * Title::countAuthorsBetween and Title::getAuthorsBetween have been deprecated.
   Use respective methods in RevisionStore instead.
+* Remove deprecated SkinCopyrightFooter &$forContent parameter
 * …
 
 === Other changes in 1.35 ===

docs/hooks.txt

@@ -3049,8 +3049,6 @@ $type: 'normal' or 'history' for old/diff views
 &$msg: overridable message; usually 'copyright' or 'history_copyright'. This
   message must be in HTML format, not wikitext!
 &$link: overridable HTML link to be passed into the message as $1
-&$forContent: DEPRECATED! overridable flag if copyright footer is shown in
-  content language.
 
 'SkinEditSectionLinks': Modify the section edit links
 $skin: Skin object rendering the UI

includes/skins/Skin.php

@@ -879,13 +879,7 @@ abstract class Skin extends ContextSource {
 		}
 
 		// Allow for site and per-namespace customization of copyright notice.
-		// @todo Remove deprecated $forContent param from hook handlers and then remove here.
-		$forContent = true;
-
-		Hooks::run(
-			'SkinCopyrightFooter',
-			[ $this->getTitle(), $type, &$msg, &$link, &$forContent ]
-		);
+		Hooks::run( 'SkinCopyrightFooter', [ $this->getTitle(), $type, &$msg, &$link ] );
 
 		return $this->msg( $msg )->rawParams( $link )->text();
 	}