Fix plotting warnings in Pytest, add news for removal of six support (#215)

* Add news and fix warnings

* Add back original file content

Author: bobleesj

news/six.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* six dependency in run.txt
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

news/warning.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* two warnings with (1) linestyle redundantly defined and (2) no artists with labels found to put in legend
+
+**Security:**
+
+* <news item>

src/diffpy/pdfgui/gui/extendedplotframe.py

@@ -182,9 +182,10 @@ def insertCurve(self, xData, yData, style):
         style -- the way curve should be plotted
         return:  internal reference to the newly added curve
         """
-        stylestr, properties = self.__translateStyles(style)
-        curveRef = self.subplot.plot(xData, yData, stylestr, **properties)[0]
-        self.subplot.legend(**legendBoxProperties())
+        _, properties = self.__translateStyles(style)
+        curveRef = self.subplot.plot(xData, yData, **properties)[0]
+        if "legend" in style:
+            self.subplot.legend(**legendBoxProperties())
         try:
             self.datalims[curveRef] = (min(xData), max(xData), min(yData), max(yData))
         except ValueError: