Drops custom PyPI for securedrop-export

Updated the build logic for securedrop-export to remove use of the
https://pypi.securedrop.org URL. At present, the securedrop-export
doesn't use any external Python dependencies, it's core-only. So the
custom PyPI URL was never necessary, and technically we could excise it
altogether right now, but for consistency's sake I'm updating it to
match the other Python-based SDW packages.

Makefile

@@ -26,7 +26,7 @@ securedrop-workstation-viewer: ## Builds Debian metapackage for Disposable VM de
 
 .PHONY: securedrop-export
 securedrop-export: ## Builds Debian package for Qubes Workstation export scripts
-	PKG_NAME="securedrop-export" ./scripts/build-debianpackage
+	WHEELS_DIR="$(PWD)/localwheels/" PKG_NAME="securedrop-export" ./scripts/build-debianpackage
 
 .PHONY: securedrop-log
 securedrop-log: ## Builds Debian package for Qubes Workstation securedrop-log scripts

README.md

@@ -34,8 +34,8 @@ Maintainers of `securedrop-client` and `securedrop-proxy` must ensure that
 the requirements files which are used for build of these packages (`build-requirements.txt`)
 using `make requirements` are kept up to date in latest `main` of those repositories.
 
-If new dependencies were added in the `requirements.txt` of that
-repo that are not in the FPF PyPI mirror (https://pypi.securedrop.org/), then the maintainer needs
+If new dependencies were added in the `build-requirements.txt` of that
+repo that are not in the FPF PyPI mirror (`./localwheels/` in this repository), then the maintainer needs
 to do the following (we are taking `securedrop-client` project as example):
 
 ### 0. Create updated build-requirements.txt for the project

securedrop-export/debian/rules

@@ -7,8 +7,10 @@ override_dh_virtualenv:
 	dh_virtualenv \
 		--python /usr/bin/python3 \
 		--setuptools \
-		--index-url https://pypi.securedrop.org/simple \
 		--extra-pip-arg "--ignore-installed" \
+		--extra-pip-arg "--no-index" \
+		--extra-pip-arg "--find-links" \
+		--extra-pip-arg "$(WHEELS_DIR)" \
 		--extra-pip-arg "--no-deps" \
 		--extra-pip-arg "--no-cache-dir" \
 		--extra-pip-arg "--no-use-pep517" \