Removed inactive Linkedin API

As per requested @marekdano

As requested by the reviewer PR updated in order to fix API duplication and missing https for hubblesite.

Indeed has discontinued their API. See https://stackoverflow.com/a/66036140/13752077

The PR #1610 added an duplicate link to the government section

The PR #1610 added an extra blank line

This isn't an API but rather the site where they are collated by the UK
government.

I've added the data.gov.uk site as a separate entry for clarity (because
of the number of similar sites from other countries). This site is also
linked to from the API catalogue site.

Fixes the issue #1307

The links https://plino.herokuapp.com and https://sentim-api.herokuapp.com were broken

Mozilla Observatory ordered alphabetically

This description broken tests:

- description should not end with .
- description should not exceed 100 characters (currently 131)

Close #1095

Close #999

Closes #1597