Remove workaround for CMake < 3.1.0 (HOOMD requires >=3.9).
Remove workaround for CMake < 3.1.0 (HOOMD requires >=3.9).

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue