plugin cleanup re: phpstan 1.0 warnings

plugins/af_comics/init.php

plugins/af_redditimgur/init.php

plugins/af_youtube_embed/init.php

plugins/af_zz_vidmute/init.php

plugins/auth_internal/init.php

plugins/auth_remote/init.php

plugins/auto_assign_labels/init.php

plugins/hotkeys_force_top/init.php

plugins/hotkeys_noscroll/init.php

plugins/hotkeys_swap_jk/init.php

plugins/no_iframes/init.php

plugins/note/init.php

plugins/shorten_expanded/init.php

plugins/toggle_sidebar/init.php