Remove wagtail-cache and wagtail-purge (#4000)

Procfile

docs/setup/deployment/production/stand-alone.md

hypha/home/models.py

...igrations/0001_add_investments_table_and_partners_page.py

hypha/settings/base.py

hypha/settings/dev.py

hypha/settings/django.py

hypha/settings/local.py.example

requirements.txt