build: fix the 'update working copy' step in Easy Build so it doesn't create a detached HEAD anymore.
build: no longer fix 'colophon' invocation in binutils because it's fixed upstream.

This was added to fix an issue where systems with texinfo >= 5.0 would
break while building binutils as we were building a pre-2.23 version. Now
that we are using a recent bintuils, this has been resolved, and the sed
command actually breaks the working invocation now.