arm: mvebu: Remove theadorable_defconfig

Currently, we support 2 "theadorable" MVEBU build targets. One with a
stripped down configuration (theadorable) and one with a full blown
configuration (theadorable_debug), including PCI, ethernet etc. When
we introduced these configs, the plan was to remove the debug version
at some point. But now it seems better to keep the full-blown version
and remove the "non-debug" version instead.

At a later stage, I will rename the remaining "theadorable_debug"
target into a more fitting one.

Signed-off-by: Stefan Roese <sr@denx.de>