Simplifying conditionals in preparation for adding another dynamic route
for a group members page.

I was looking into tackling the TODO comment for the location prop¹ in
the groups JS routing. The location prop was being passed around to be
used in the NavBar component, but the use of it was removed in a
recent refactoring.² So just remove all of the unused `location` props
for the `NavBar` and the `GenericPage` components.

¹ <https://github.com/nextstrain/nextstrain.org/blob/1aeb1e499b9f25d9a918465fd3450fca51f40a2d/static-site/pages/groups/%5B...groupName%5D.jsx#L22>
² <ac12e32>

The OPTIONS method was included in the RESTful API docs¹ for the new
Groups membership routes, but were not added to the routes themselves.

I will be using this in future changes to check user permissions for
viewing and editing Group members.

¹ <84a7374#diff-676fb03989c04d3661eac5e82cb55fc6a9f43df70bd94565535ba509e12f0c64>

The new page is available at `groups/<groupName>/settings/members`.
I chose to use the same URL as the API so that we don't have to take
up another namespace (e.g. `groups/<groupName>/members`). The main Group
page will only link out to the members page if the current user is
authorized to list Group members.

The members list only displays the most privileged role for each member
to keep the display simple. It assumes the group roles API returns the
roles in the order from least to most privileged.

- remove unused `props`
- remove unnecessary semicolons

Based on feedback from @victorlin in review
<#973 (comment)>

Based on feedback from @victorlin in review
<#973 (comment)>

Based on feedback from @genehack
<#973 (comment)>

Based on feedback from @tsibley
<#973 (comment)>