This is a followup to 99c45877a984dd0148151b2e304afef6fb04f1a5, which
introduced a regression: "guix system build gnu/system/install.scm"
would fail to find the .tmpl files.
* gnu/system/install.scm (/etc/configuration-files)[file]: Remove.
[directory]: Use 'local-file' with a literal string.