[!!!][TASK] Remove deprecated adminpanel/feedit code

The following previously deprecated classes/interfaces have been removed:

* TYPO3\CMS\Adminpanel\View\AdminPanelView
* TYPO3\CMS\Adminpanel\View\AdminPanelViewHookInterface
* TYPO3\CMS\Core\FrontendEditing\FrontendEditingController

The following methods have been removed:
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->initializeAdminPanel()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->initializeFrontendEdit()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->isFrontendEditingActive()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->displayAdminPanel()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->isAdminPanelVisible()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->checkBackendAccessSettingsFromInitPhp()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->extPageReadAccess()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->extGetTreeList()
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->extGetLL()

The following public properties have been removed
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->extAdmEnabled
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->adminPanel
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->frontendEdit
* TYPO3\CMS\Backend\FrontendBackendUserAuthentication->extAdminConfig

The following PageTSconfig option has no effect anymore:
* TSFE.frontendEditingController

Resolves: #87231
Releases: master
Change-Id: I88cc3ac18077f054cc8895f5ccfb65291e94defa
Reviewed-on: https://review.typo3.org/59205


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>