[pkg] Remove build dependency on dh-systemd
As suggested by Lintian, remove build dependency on obsolete package
dh-systemd. Instead, specify a more precise version of debhelper 9 that
added support for systemd.
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pygments_style = sphinx.pygments_styles.PyramidStyle
stylesheet = cubicweb.css
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logo = logo-cubicweb.svg
favicon = cubicweb.ico
in_progress = false
outdated = false
canonical_url =