Drop debian/compat and switch to debhelper-compat approach Fixes: | dh_clean | dh_clean: error: Compatibility levels before 7 are no longer supported (level 5 requested) Also replace `dh_clean -k` with `dh_prep`, to then fix: | dh_clean -k | dh_clean: warning: The -k option is not supported in compat 12; use dh_prep instead | dh_clean: error: This feature was removed in compat 12.