Tweak doc Makefile clean target?

[greschd]

In the Makefile clean target for the docs (Python), the following line

ansys-templates/src/ansys/templates/python/common/{{cookiecutter.__project_name_slug}}/doc/Makefile

Line 24 in ffdf51d

rm -rf $(BUILDDIR)/*

bugs me a little bit.. due to what happens when BUILDDIR is not set.

Of course, "who would ever think to unset BUILDDIR"? Well...

Removing the /* bit should be enough to fix that problem.