Remove largely unmaintained Mihawk

A fork of it is maintained but its upstream layer has largely been
unmaintained.
No future products are planned to be based on this layer.
Mihawk is similar to Witherspoon.

Signed-off-by: Myung Bae <myungbae@us.ibm.com>
Change-Id: I82f7d777b78cd126237d51e42f1e11abdf80ae68