bpo-39600, IDLE: Remove duplicated font names (GH-18430)

In the font configuration window, remove duplicated font names.
(cherry picked from commit ed335cf)

Co-authored-by: Victor Stinner <[email protected]>

Author: miss-islington

Lib/idlelib/configdialog.py

@@ -607,8 +607,9 @@ def load_font_cfg(self):
         font_bold  = configured_font[2]=='bold'
 
         # Set editor font selection list and font_name.
-        fonts = list(tkFont.families(self))
-        fonts.sort()
+        fonts = tkFont.families(self)
+        # remove duplicated names and sort
+        fonts = sorted(set(fonts))
         for font in fonts:
             self.fontlist.insert(END, font)
         self.font_name.set(font_name)

Misc/NEWS.d/next/IDLE/2020-02-10-17-09-48.bpo-39600.X6NsyM.rst

@@ -0,0 +1 @@
+In the font configuration window, remove duplicated font names.