Update mkdocs.yml

[bbfrederick]

Remove the "Libraries" item from the Libraries menu

Closes #53

Proposed Changes

Change Type

• [ x] bugfix
• refactoring
• infrastructure
• documentation
• other

Checklist before review

• [ x] I added everything I wanted to add to this PR.
• [Documentation only] I built the docs locally.
• My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• My code respects the adopted style, especially linting conventions.
• The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• I added or indicated the right labels.

• I added information regarding the timeline of completion for this PR.

• Please, comment on my PR while it's a draft and give me feedback on the development!

[m-miedema]

Good catch!