I know the wfDeprecated() has already been removed, but anyway…
Couldn't you just create a MyExtensionNameSpecialPage class like below and extend that for your special pages instead of regular SpecialPage, which would let you always call the non-deprecated getPageTitle() instead of getTitle() even on ancient MediaWiki versions?
class MyExtensionNameSpecialPage extends SpecialPage { function getPageTitle( $subpage = false ) { return self::getTitleFor( $this->mName, $subpage ); } }
($mName is protected, so this is fine, but you can always use getName() instead.)