Drop link to license file in pyproject (#406)

This was trying to insert the full license text in the sidebar on PyPI. Try to
avoid that.

Author: BrianJKoopman

pyproject.toml

@@ -10,7 +10,6 @@ name = "ocs"
 dynamic = ["version"]
 description = "Observatory Control System"
 readme = "README.rst"
-license = {file = "LICENSE.txt"}
 requires-python = ">=3.7"
 classifiers = [
     "Framework :: Twisted",