Rename `VERSIONS_TO_REMOVE_IN_x` constant from 17_0 to 18_0
What does this MR do and why?
This MR renames a constant called VERSIONS_TO_REMOVE_IN_17_0
to VERSIONS_TO_REMOVE_IN_18_0
as the GitLab version is already greater than 17.0 and keeping the old constant name can be astonishing.
Related to Change `VERSIONS_TO_REMOVE_IN_17_0` constant to... (#438260 - closed).