Remove NEWS.rst from the long description

The entries for version 0.5.0 include a :math: directive. This is not
supported by readme_renderer, which causes the package upload to fail.

setup.cfg

@@ -6,7 +6,8 @@ project-urls =
     Documentation = https://pypfilt.readthedocs.io/en/latest/
     Changelog = https://pypfilt.readthedocs.io/en/latest/changelog.html
 description = Bootstrap particle filter for epidemic forecasting
-long_description = file: README.rst, NEWS.rst
+long_description = file: README.rst
+long_description_content_type = text/x-rst
 license = BSD 3-Clause License
 license_file = LICENSE
 author = Rob Moss