[web] Remove remnants of SquadCal "Request Access" functionality

Summary: Removed the React side of this earlier, but looks like I missed the keyserver functionality. Found this change stashed in my local environment

Test Plan: Made sure our current landing page SubscriptionForm component continues to work as expected... they're two separate endpoints (subscribe_email for landing subscription form, request_access for "legacy" request access form)

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

Subscribers: Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3937