pkg_resources is deprecated as an API

[phargogh]

When I run the SDR tests, I see some warnings that look like this:

============================================================================================================================ test session starts =============================================================================================================================
platform darwin -- Python 3.10.8, pytest-7.2.2, pluggy-1.0.0
rootdir: /Users/jdouglass/workspace/phargogh/invest, configfile: pytest.ini
plugins: xdist-3.2.1, anyio-3.6.2
collected 14 items

tests/test_sdr.py ..............                                                                                                                                                                                                                                       [100%]

============================================================================================================================== warnings summary ==============================================================================================================================
tests/test_sdr.py::SDRTests::test_base_regression
  /Users/jdouglass/workspace/phargogh/invest/env310/lib/python3.10/site-packages/pkg_resources/__init__.py:121: DeprecationWarning: pkg_resources is deprecated as an API
    warnings.warn("pkg_resources is deprecated as an API", DeprecationWarning)

tests/test_sdr.py::SDRTests::test_base_regression
tests/test_sdr.py::SDRTests::test_base_regression
tests/test_sdr.py::SDRTests::test_base_regression
tests/test_sdr.py::SDRTests::test_base_regression
  /Users/jdouglass/workspace/phargogh/invest/env310/lib/python3.10/site-packages/pkg_resources/__init__.py:2870: DeprecationWarning: Deprecated call to `pkg_resources.declare_namespace('sphinxcontrib')`.
  Implementing implicit namespace packages (as specified in PEP 420) is preferred to `pkg_resources.declare_namespace`. See https://setuptools.pypa.io/en/latest/references/keywords.html#keyword-namespace-packages
    declare_namespace(pkg)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================================================================================================================= 14 passed, 5 warnings in 3.82s =======================================================================================================================

I'm not sure what to do about the sphinx warnings, but the others are all raised during from natcap.invest import sdr because we import pkg_resources within natcap/invest/__init__.py, as verified by a stack trace. The recommended way to read the version has changed, per the setuptools_scm docs: https://setuptools-scm.readthedocs.io/en/latest/usage/