Stop converting exercise math using mathmlcloud in assemble
Stop converting exercise math using mathmlcloud in assemble

In "neb assemble", we fetch exercises and then try to convert the math
using mathmlcloud.cnx.org.  It makes "neb assemble" very slow when there
are lots of exercises with math, e.g. hsphysics (col10002 on content04).
Since "neb assemble" is part of the bakery CLI, we can just leave the
math until the mathify step instead.  This speeds up "neb assemble" for
hsphysics by more than 50% (from 20m to 9m) on my machine.

Connexions/nebuchadnezzar