Revert "Install synapse-http-antispam from pypi"

This reverts commit 8681621d.

Dockerfile

@@ -33,7 +33,7 @@ RUN pip install --prefix="/install" --no-warn-script-location --ignore-installed
  && pip install --prefix="/install" --no-warn-script-location \
         --no-deps \
 	'synapse-simple-antispam @ git+https://github.com/maunium/synapse-simple-antispam' \
-	synapse-http-antispam \
+	'synapse-http-antispam @ git+https://github.com/maunium/synapse-http-antispam' \
 	'shared_secret_authenticator @ git+https://github.com/devture/matrix-synapse-shared-secret-auth@2.0.3' \
  && pip install --prefix="/install" --no-warn-script-location \
         --no-deps /synapse