Update content for redesigned Meeting Calendar plugin

[adamwoodnz]

When the Meeting Calendar redesign PR is merged most of the styles we added to the Learn 2024 theme will not be required anymore.

This PR removes all the custom styles, and some content which is now rendered by plugin. Only styles for hiding specific elements not relevant to Learn remain.

See #2944

Changes

1. The previous and next navigation buttons have changed in the plugin
2. The team filter is hidden. We were relying on no teams being set, but some more have been added, so the dropdown started to be shown again. I believe these are not useful and are probably data entry mistakes:

3. 'Events are shown in your local time zone.' has been extracted from the copy at the bottom as this is now rendered by the plugin. Same goes for the feed links.

Before	After

Testing

Best tested in sandbox.

1. Load this branch and Redesign calendar frontend meeting-calendar#159
2. Test calendar view and list view for regressions. Include modal event details for calendar view
3. Test feed links
4. Test responsiveness