debian: Use dh_installsystemduser

Closes: #10
7 jobs for master in 6 minutes and 19 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #331436
librem5
build:native:bullseye

00:01:02

passed #331435
librem5
build:native:buster

00:00:54

 
  Package
passed #331439
librem5:arm64
package:deb-debian-bullseye:arm64

00:03:36

passed #331437
librem5
package:deb-debian-buster

00:02:09

passed #331438
librem5:arm64
package:deb-debian-buster:arm64

00:03:37

 
  Test Package
passed #331440
librem5
autopkgtest-debian-buster-package

00:01:33

passed #331441
librem5
lintian-debian-buster-package

00:01:37