Fix some of the Javascript linting issues, as well as bugs and unneeded divergences with upstream (#2208)

* Run eslint --fix

* Fix linting issues in video player and reduce divergences with upstream

This includes a behavior change of not auto-looping videos anymore. I don't
remember loops being ever intended, and they have been removed from upstream
a while ago, but we somehow missed the change.

* Fix lint issues in `app/javascript/flavours/glitch/selectors/index.js`

Those were basically caused by dead code that isn't present upstream, so
that brings us closer to upstream as well.

* Fix linting issue and bug in streaming/index.js

* Fix linting issues in config/webpack/shared.js

* Fix unused import in flavours/glitch/features/ui/index.js

* Fix linting issues and reduce divergences from upstream in flavours/glitch/features/ui/components/video_modal.jsx

* Fix linting issues in flavours/glitch/reducers

* Fix linting issues in glitch-soc onboarding modal

* Fix linting issues in flavours/glitch/features/ui/components/navigation_panel.jsx

* Remove dead code for unused local setting navbar_under

* Fix various linting issues

* Fix linting issues in flavours/glitch/components/scrollable_list.jsx and reduce divergences with upstream

app/javascript/flavours/glitch/features/compose/containers/options_container.js

@@ -9,7 +9,6 @@ import {
 import { openModal } from 'flavours/glitch/actions/modal';
 
 function mapStateToProps (state) {
-  const spoilersAlwaysOn = state.getIn(['local_settings', 'always_show_spoilers_field']);
   const poll = state.getIn(['compose', 'poll']);
   const media = state.getIn(['compose', 'media_attachments']);
   const pending_media = state.getIn(['compose', 'pending_media_attachments']);
@@ -18,7 +17,6 @@ function mapStateToProps (state) {
     resetFileKey: state.getIn(['compose', 'resetFileKey']),
     hasPoll: !!poll,
     allowMedia: !poll && (media ? media.size + pending_media < 4 && !media.some(item => ['video', 'audio'].includes(item.get('type'))) : pending_media < 4),
-    hasMedia: media && !!media.size,
     allowPoll: !(media && !!media.size),
     showContentTypeChoice: state.getIn(['local_settings', 'show_content_type_choice']),
     contentType: state.getIn(['compose', 'content_type']),