MNT: Remove network marker from pytest

There are no tests that need network access, so remove the marker.

Author: greglucas

lib/matplotlib/testing/conftest.py

@@ -17,7 +17,6 @@ def pytest_configure(config):
          "style: Set alternate Matplotlib style temporarily (deprecated)."),
         ("markers", "baseline_images: Compare output against references."),
         ("markers", "pytz: Tests that require pytz to be installed."),
-        ("markers", "network: Tests that reach out to the network."),
         ("filterwarnings", "error"),
         ("filterwarnings",
          "ignore:.*The py23 module has been deprecated:DeprecationWarning"),