Remove bio_html and cached_markdown_version from user_details

What does this MR do and why?

Solves https://gitlab.com/gitlab-org/gitlab/-/issues/340190

This MR removes bio_html and cached_markdown_version columns from user_details table (step two of a process) and stops exposing bio_html in API.

== 20211004151202 RemoveBioHtmlFromUserDetails: migrating =====================
-- remove_column(:user_details, :bio_html, :text, {:null=>true})
   -> 0.0018s
-- remove_column(:user_details, :cached_markdown_version, :integer, {:null=>true})
   -> 0.0008s
== 20211004151202 RemoveBioHtmlFromUserDetails: migrated (0.0027s) ============

== 20211004151202 RemoveBioHtmlFromUserDetails: reverting =====================
-- add_column(:user_details, :cached_markdown_version, :integer, {:null=>true})
   -> 0.0023s
-- add_column(:user_details, :bio_html, :text, {:null=>true})
   -> 0.0013s
== 20211004151202 RemoveBioHtmlFromUserDetails: reverted (0.0187s) ============

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