Use CMake's builtin FindPythonLibs instead of pybind11's

Podhorszki, Norbertrequested to merge
github/fork/chuckatkins/rework-python-dependencies into master

Created by: chuckatkins

The FindPythonLibNew module in pybind11 is lacking any validation of actually finding the component's it's looking for.

Fixes #306 (closed)

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