Remove unused numpy function in docs conf.py

[braingram]

asdf-wcs-schemas/docs/conf.py

Line 36 in 9557b17

numpy.random.seed(int(os.environ["SOURCE_DATE_EPOCH"]))

Is unused as seen with the test PR: #52
This could be removed with no effect on the built documentation published on readthedocs and allow this package to have no uses of numpy.

The same is likely true for other asdf schema packages.