Remove unused import statements

apps/comments/lib/Activity/Listener.php

apps/comments/lib/EventHandler.php

apps/dav/lib/CalDAV/CalDavBackend.php

apps/dav/lib/CalDAV/Plugin.php

apps/dav/lib/CalDAV/Principal/Collection.php

apps/dav/lib/CalDAV/Schedule/IMipPlugin.php

apps/dav/lib/CardDAV/CardDavBackend.php

apps/dav/lib/CardDAV/ImageExportPlugin.php

apps/dav/lib/CardDAV/Plugin.php

apps/dav/lib/Connector/LegacyDAVACL.php

apps/dav/lib/Connector/Sabre/ObjectTree.php

apps/dav/lib/Connector/Sabre/Principal.php

apps/dav/lib/Connector/Sabre/QuotaPlugin.php

apps/dav/lib/Connector/Sabre/ServerFactory.php

apps/dav/lib/DAV/SystemPrincipalBackend.php

apps/dav/lib/Files/FilesHome.php

apps/dav/lib/Files/RootCollection.php

apps/dav/lib/Server.php

apps/dav/lib/Upload/ChunkingPlugin.php

apps/encryption/lib/AppInfo/Application.php