Now that all port tests live under testsuite/sim/*/, and none live
in testsuite/ directly, flatten the structure by moving all of the
dirs under testsuite/sim/ to testsuite/ directly.
We need to stop passing --tool to dejagnu so that it searches all
dirs and not just ones that start with "sim". Since we have no
other dirs in this tree, and no plans to add any, should be fine.
