signup removal progress

config/custom-environment-variables.json

config/default.json

scripts/send_waiting_list_invites.js

src/db/models/identity.js

src/db/models/user.js

src/db/utils/find_user.js

src/server/api/general.js

src/server/sign_up_pages/enter_confirm_email.jsx

src/server/sign_up_pages/enter_confirm_mobile.jsx