MNT: Remove outdated CartoPy work-around (Fixes #1229)

This was working around CartoPy <=0.14.3 issues for transforming
vectors. Latest CartoPy is 0.17.0. 0.15.0 is almost 3 years old at this
point, I think we can rely on it.

setup.cfg

@@ -53,7 +53,7 @@ where = src
 [options.extras_require]
 dev = ipython[all]>=3.1
 doc = sphinx>=2.1; sphinx-gallery>=0.4; doc8; m2r; netCDF4
-examples = cartopy>=0.13.1; matplotlib>=2.2.0; pyproj>=1.9.4,!=2.0.0
+examples = cartopy>=0.15.0; matplotlib>=2.2.0; pyproj>=1.9.4,!=2.0.0
 test = pytest>=2.4; pytest-mpl; pytest-flake8; cartopy>=0.16.0; flake8>3.2.0; flake8-builtins!=1.4.0; flake8-comprehensions; flake8-copyright; flake8-docstrings; flake8-import-order; flake8-mutable; flake8-pep3101; flake8-print; flake8-quotes; flake8-rst-docstrings; pep8-naming; netCDF4; pyproj>=1.9.4,!=2.0.0
 
 [build_sphinx]

src/metpy/plots/station_plot.py

@@ -5,7 +5,6 @@
 
 from enum import Enum
 
-import matplotlib
 import numpy as np
 
 from .wx_symbols import (current_weather, high_clouds, low_clouds, mid_clouds,
@@ -276,20 +275,7 @@ def plot_barb(self, u, v, **kwargs):
         if self.barbs:
             self.barbs.remove()
 
-        # Handle transforming our center points. CartoPy doesn't like 1D barbs
-        # TODO: This can be removed for cartopy > 0.14.3
-        if hasattr(self.ax, 'projection') and 'transform' in kwargs:
-            trans = kwargs['transform']
-            try:
-                kwargs['transform'] = trans._as_mpl_transform(self.ax)
-            except AttributeError:
-                pass
-            u, v = self.ax.projection.transform_vectors(trans, self.x, self.y, u, v)
-
-            # Since we've re-implemented CartoPy's barbs, we need to skip calling it here
-            self.barbs = matplotlib.axes.Axes.barbs(self.ax, self.x, self.y, u, v, **defaults)
-        else:
-            self.barbs = self.ax.barbs(self.x, self.y, u, v, **defaults)
+        self.barbs = self.ax.barbs(self.x, self.y, u, v, **defaults)
 
     def plot_arrow(self, u, v, **kwargs):
         r"""At the center of the station model plot wind arrows.
@@ -328,21 +314,7 @@ def plot_arrow(self, u, v, **kwargs):
         if self.arrows:
             self.arrows.remove()
 
-        # Handle transforming our center points. CartoPy doesn't like 1D arrows
-        # TODO: This can be removed for cartopy > 0.14.3
-        if hasattr(self.ax, 'projection') and 'transform' in kwargs:
-            trans = kwargs['transform']
-            try:
-                kwargs['transform'] = trans._as_mpl_transform(self.ax)
-            except AttributeError:
-                pass
-            u, v = self.ax.projection.transform_vectors(trans, self.x, self.y, u, v)
-
-            # Since we've re-implemented CartoPy's arrows, we need to skip calling it here
-            self.arrows = matplotlib.axes.Axes.quiver(self.ax, self.x, self.y, u, v,
-                                                      **defaults)
-        else:
-            self.arrows = self.ax.quiver(self.x, self.y, u, v, **defaults)
+        self.arrows = self.ax.quiver(self.x, self.y, u, v, **defaults)
 
     @staticmethod
     def _plotting_units(u, v, plotting_units):