Remove 'Show key events only' filter in liveblogs

[petternitter]

Context

Currently, the liveblogs feature a carousel outlining key events and links through to the relevant blocks as well as a filter toggle to only display those key event blocks, removing all other blocks.

Only 0.15% of views of the liveblog utilise the filter toggle, likely because the two features fulfil much of the same user need (i.e. getting up to speed on key events that have already happened when entering the blog).

The purpose of this ticket is to remove the filter toggle UI and associated functionality (i.e. mechanism that allows for filtering), retaining only the key events carousel and functionality that links through to relevant blocks.

Priority

Not urgent; the feature works but given low usage we are primarily removing it to reduce maintenance overhead.

[petternitter]

Jon Haynes and Claire Phipps have been made aware of usage stats and are happy for us to proceed with removing this feature.