Small improvement for nicer unit-testing

In case you just run "make htools/test" to recompile the unittests,
the old .tix file should be removed, otherwise you get the message
about inconsistent tick boxes. Let's make the compilation process
automatically remove this, for easier testing.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>