Don't install setuptools-scm==6.0.1 via override_dh_autoinstall

setuptools-scm 6.0.1 has an unbounded setuptools build dependency, that has
started to pull in a breaking version of setuptools. As far as i can tell, package
wheel builds aren't using it anyway - build isolation means they pull in their
ownn versions of everything. So we can just not install it.

AFAICT this doesn't affect the current state (lack) of build reproducibility. Any
improvements there would probably mean building and using our own wheels following
the same pattern as securedrop-builder&securedrop-client

securedrop/debian/rules

@@ -25,8 +25,6 @@ override_dh_auto_install:
 	python3 /srv/redwood/build-wheel.py --release --redwood /srv/redwood --target /srv/redwood/target
 	# Set up virtualenv and install dependencies
 	/usr/bin/python3 -m venv ./debian/securedrop-app-code/opt/venvs/securedrop-app-code
-	./debian/securedrop-app-code/opt/venvs/securedrop-app-code/bin/pip install $(PIP_ARGS) \
-		setuptools-scm==6.0.1
 	./debian/securedrop-app-code/opt/venvs/securedrop-app-code/bin/pip install $(PIP_ARGS) \
 		pip==21.3
 	./debian/securedrop-app-code/opt/venvs/securedrop-app-code/bin/pip install $(PIP_ARGS) \