drop studip-checkbox CSS class, fixes #111

app/views/admin/configuration/type-edit.php

app/views/admin/courseplanning/pick_color.php

app/views/admin/courseplanning/viewcolumns.php

app/views/admin/install/mysql.php

app/views/admin/install/prepare.php

app/views/consultation/admin/cancel_slot.php

app/views/consultation/admin/index.php

app/views/consultation/admin/ungrouped.php

app/views/files/_fileref_tr.php

app/views/files/_files_thead.php

app/views/files/_folder_tr.php

app/views/help_content/admin_overview.php

app/views/profile_modules/index.php

app/views/resources/property/_add_edit_form.php

app/views/resources/room_request/_add_edit_form.php

resources/assets/stylesheets/less/forms.less

resources/assets/stylesheets/less/skiplinks.less

resources/assets/stylesheets/scss/installer.scss

resources/vue/components/FilesTable.vue

resources/vue/components/StudipProxiedCheckbox.vue