As of
https://gitlab.com/postmarketOS/ci-common/-/commit/666df6d1333ee1699d13bf6f75ab0f66b78aaa42
the default pmbootstrap version used is master, not 2.3.x. As such,
let's avoid duplicating that downstream.

Closes https://gitlab.com/postmarketOS/pmbootstrap/-/issues/2396

This reverts commit 7a930582.