levels: Delete unused levels

These are no longer used to build the main IWADs (exempting
catoptromancy/fdtest.wad from this sweep), and are being moved to the
attic repo.
levels: move map06 to its proper location

Catoptromancy made fixes to the map previously, but did not originally
author it, moving it back to mystic.
levels: move map14 to its proper location

Catoptromancy made fixes to the map previously, but did not originally
author it, moving it back to thegreenherring.