Remove Optional from Link.show_url
Remove Optional from Link.show_url

Since we're moving functions to a file with stricter typing, this
prevents mypy from complaining that our string is possibly None.

xavfernandez/pip,sbidoul/pip,xavfernandez/pip,pradyunsg/pip,pradyunsg/pip,pypa/pip,xavfernandez/pip,pypa/pip,pfmoore/pip,sbidoul/pip,pfmoore/pip