Switch default to byzantium

We use the unencrypted image since it's smaller and want to
add the a helper to change the encryption key to avoid
a false sense of security.

Closes: #1
6 jobs for byzantium in 4 minutes and 24 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed test:check #365854
librem5

00:00:51

passed test:download:pip #365853
librem5

00:02:10

 
  Package
passed package-pureos-byzantium #365855
librem5

00:00:38

passed package-pureos-byzantium:arm64 #365856
librem5:arm64

00:02:14

 
  Test Package
passed autopkgtest-pureos-byzantium-package #365857
librem5

00:00:46

passed lintian-pureos-byzantium-package #365858
librem5

00:00:40