Issue #25494: Remove extra quote from docstring.

Patch by John Mark Vandenberg.
diff --git a/Lib/statistics.py b/Lib/statistics.py
index 25a26d4..a56f91f 100644
--- a/Lib/statistics.py
+++ b/Lib/statistics.py
@@ -360,7 +360,7 @@
 
 
 def median_grouped(data, interval=1):
-    """"Return the 50th percentile (median) of grouped continuous data.
+    """Return the 50th percentile (median) of grouped continuous data.
 
     >>> median_grouped([1, 2, 2, 3, 4, 4, 4, 4, 4, 5])
     3.7