FindRuby: Remove documentation for non-existent Ruby_ROOT_DIR
Documentation was added by !4386 (merged), but this feature was never implemented.
Closes: #21528 (closed)
Backport: release
Topic-rename: FindRuby-doc-fix
Edited by Brad King
System updates will be applied on May 27th between 7am and 9am, EST (UTC-05:00). This site will have intermittent downtime during that time.
Documentation was added by !4386 (merged), but this feature was never implemented.
Closes: #21528 (closed)
Backport: release
Topic-rename: FindRuby-doc-fix