Only curate specs that have a good standing

[tidoust]

This leverages the standing property in browser-specs to exclude specs that don't have a good standing from data curation.

This makes it possible to add specs to browser-specs at an earlier level for cross-referencing purpose (Specref and terms) without having to worry too much about its impact on CSS, elements, events, and IDL definitions. It also makes it possible to keep discontinued specs in browser-specs without having to worry about extracts becoming obsolete, invalid, or conflictual.

This is intended to replace #712 with a different exclusion logic. In #712, specs that were excluded from data curation were the ones that did not target browsers, based on the categories property. This does not help with the main source of CSS, events and IDL hiccups, which are more common in early API proposals. Plus I still think that filtering specs based on their categories is not the right approach.

This will remove the following curated extracts:

• CSS extract of CSS Conditional Values Module Level 1
• CSS extract of Non-element Selectors Module Level 1
• IDL extract of Direct Sockets API. If we want to keep the IDL, the right mechanism would be to drop the "pending" standing, but the spec itself says that it is an unofficial draft.
• IDL extract of Web Publications, which seems a good thing given that the spec has been discontinued.
• IDL extract of Document Object Model (DOM) Level 2 Style, which we were previously doing through a patch.

This does not add any mechanism to create exceptions to the rule. That is on purpose. Let's be optimistic ;)

Note the plan to also make Reffy skip "discontinued" specs by default, in w3c/reffy#1341. With these two updates, the workflow becomes:

1. Specs that are in good standing are crawled and curated
2. Specs that have a pending standing are crawled but not curated
3. Specs that have been discontinued are not crawled by default (but may be for legacy/cross-referencing purpose) and not curated.

The rule for inclusion in NPM packages does not change: only specs targeted at browsers are included.