temp/eg25-manager: fork from alpine to upgrade to git version, which deals with ofono

git master of eg25-manager has patches merged, that make it work with ofono. I've asked for an official release a few days ago, but apparently it will take a bit longer until there is one. As the postmarketOS v21.03 release is very close, just package that git version for now, and backport it to v21.03.

A second patch drops the ofono specific setup-modem.sh script, which is no longer necessary. The AT commands are sent by eg25-manager now.