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

This reverts commit 73abb573feae03b164d3ed4284db4ed4ff26a256.
Revert "Make sure functions called by rc.start_packages can see $g['booting'] when we are booting"

This reverts commit 5eb99ec9fae6b6ff077559b3feab8565701f2635.
Remove /var/run/booting early to be consistent with $g['booting']