Remove unnecessary annotations from import search

[vkWeb]

Observed behavior

Currently, we are unnecessarily querying contentnode tags in import search API. We don't need to annotate content_tags since now we get that info from the public API.

Expected behavior

Remove thumbnail_extension, thumbnail_checksum and content_tags annotation code. Also remove items from field_map that are commented out in values of SearchContentNodeViewSet.

User-facing consequences

Querying content_tags has a huge impact on import search performance. Now that we are safe to remove that querying from the search API, we should gain substantial performance improvement.

Usage Details

• OS: Ubuntu 22.04
• Browser: Chrome
• URL: unstable branch

[rtibbles]

Fixed in #4279