Merge branch 'revert-updates' into 'master'

Revert "pureos: Temporarily add amber-proposed-upates"

See merge request Librem5/image-builder!135

conf/dists/amber-phone-staging

@@ -5,8 +5,6 @@ deb https://repo.pureos.net/pureos amber-security main
 deb https://repo.pureos.net/pureos amber-phone main
 deb https://repo.pureos.net/pureos amber-phone-staging main
 
-deb https://repo.pureos.net/pureos amber-proposed-updates main
-
 deb http://repo.pureos.net/pureos-debug/ amber-debug main
 deb http://repo.pureos.net/pureos-debug/ amber-phone-staging-debug main
 "