Uninstalls RPM in prep-dev script

Follow up to #587.

The `dnf install -y <local_file>` action will not reinstall a package
if the versions are the same. Since we expect package contents to
change, but not version strings, when running `make clone`, let's make
sure to uninstall the rpm package in dom0 so that the install action
always takes effect.

scripts/prep-dev

@@ -21,6 +21,8 @@ if [[ -z "$latest_rpm" ]]; then
 fi
 
 echo "Deploying Salt config..."
+echo "Uninstalling any previous rpm versions..."
+sudo dnf remove -y securedrop-worsktation-dom0-config || true
 echo "Installing RPM at $latest_rpm ..."
 sudo dnf install -y "$latest_rpm"