removed all uses of dmat-LU.hpp

This code wasn't being used anyway.  The file itself can be deleted now
(and then reused for newer code)
Changes to EngineTests.  Now 'check' passes on all of these tests

And some of the tests have been made shorter, so the whole thing doesn't
take too long to complete.
check EngineTests now takes about 90 seconds on my rMBP.

Some tests were simplified to get this down to a reasonable time