Revert "Only unset $g['booting'] when it was set here"

This reverts commit 47493bd326cd7141df7df708b69e10479ed800af.
Revert "Make sure functions called by rc.start_packages can see $g['booting'] when we are booting"

This reverts commit 8a461f41db7907b310171b6e0fb901b2f5e7e2fe.
Remove /var/run/booting early to be consistent with $g['booting']