python3-testtools: Fix build problems from incorrect build backend

python3-testtools: Fix build problems from incorrect build backend

testtools uses the hatchling backend so:
  * merge the inc back into the recipe
  * drop setuptools
  * use the hatchling backend
  * add the needed vcs dependency
  * drop the now unneeded python3-pbr dependency

This means the submodules are included in packaging, fixing build failures
and the verison in the wheel is no longer 0.0.0

Prior to this fix, testtools in buildtools tarball was completely
broken.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>