removed unnecessary dependency (#558)

ipympl/backend_nbagg.py

@@ -31,7 +31,6 @@
 from IPython import get_ipython
 from IPython import version_info as ipython_version_info
 from IPython.display import HTML, display
-from ipython_genutils.py3compat import string_types
 from ipywidgets import DOMWidget, widget_serialization
 from matplotlib import is_interactive, rcParams
 from matplotlib._pylab_helpers import Gcf
@@ -248,7 +247,7 @@ def __init__(self, figure, *args, **kwargs):
     def send_state(self, key=None):
         if key is None:
             keys = self.keys
-        elif isinstance(key, string_types):
+        elif isinstance(key, str):
             keys = [key]
         elif isinstance(key, Iterable):
             keys = key

pyproject.toml

@@ -42,7 +42,6 @@ classifiers = [
 ]
 dependencies = [
     "ipython<9",
-    "ipython_genutils",
     "ipywidgets>=7.6.0,<9",
     "matplotlib>=3.4.0,<4",
     "numpy",