Remove unused get_platform function
Remove unused get_platform function

Now handled internally in `packaging.tags` (in `_platform_tags`).

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