Merge pull request #2452 from greglucas/deprecate-clip-path

MNT: Deprecate unused clip_path module

lib/cartopy/mpl/clip_path.py

@@ -2,10 +2,17 @@
 #
 # This file is part of Cartopy and is released under the BSD 3-clause license.
 # See LICENSE in the root of the repository for full licensing details.
+import warnings
+
 import matplotlib.path as mpath
 import numpy as np
 
 
+warnings.warn('The clip_path module is deprecated and will be removed '
+              'in a future release with no replacement.',
+              DeprecationWarning, stacklevel=2)
+
+
 def intersection_point(p0, p1, p2, p3):
     """
     Returns