fix(gridintersect): removed matplotlib dependency (#643)

A recent PR added an import of gridintersect when flopy is imported.  This broke some things on the MODFLOW 6 development side and inadvertently required matplotlib, even if no plotting is needed.

flopy/utils/gridintersect.py

@@ -1,4 +1,3 @@
-import matplotlib.pyplot as plt
 import numpy as np
 from .geometry import transform
 try:
@@ -1055,6 +1054,10 @@ def plot_polygon(rec, ax=None, **kwargs):
             returns the axes handle
 
         """
+        try:
+            import matplotlib.pyplot as plt
+        except ImportError:
+            print('This feature requires matplotlib.')
         try:
             from descartes import PolygonPatch
         except ModuleNotFoundError:
@@ -1093,6 +1096,10 @@ def plot_linestring(rec, ax=None, **kwargs):
             returns the axes handle
 
         """
+        try:
+            import matplotlib.pyplot as plt
+        except ImportError:
+            print('This feature requires matplotlib.')
         if ax is None:
             _, ax = plt.subplots()
 
@@ -1130,6 +1137,10 @@ def plot_point(rec, ax=None, **kwargs):
             returns the axes handle
 
         """
+        try:
+            import matplotlib.pyplot as plt
+        except ImportError:
+            print('This feature requires matplotlib.')
         if ax is None:
             _, ax = plt.subplots()