htl: Enable more cancellation tests

* nptl/tst-cancel-self-cancelstate.c, tst-cancel-self.c, tst-cancel9.c,
tst-cancelx9.c: Move to...
* sysdeps/pthread: ... here.
* nptl/Makefile: Move corresponding references and rules to...
* sysdeps/pthread/Makefile: ... here.