This simplifies #12467.
Using a tree-exclusive amor type is far more efficient
than adding more warheads, which cost performance
due to their huge Spread
This also restores the 100% efficiency vs. trees for
some of the incendiary nuke warheads (which have
reduced efficiency vs. Wood since #13643).
Note: Atomic had two tree-only warheads with a Delay
of 15, I believe the first one to be a copy-paste error
and moved the damage to the regular SpreadDamage
with a Delay of 10.
f132bac80d