hgweb: disable cgitb by default in hgwebdir.fcgi too

contrib/hgwebdir.fcgi

@@ -9,9 +9,9 b''
 # enable demandloading to reduce startup time
 from mercurial import demandimport; demandimport.enable()
 
-# send python tracebacks to the browser if an error occurs:
-import cgitb
-cgitb.enable()
+# Uncomment to send python tracebacks to the browser if an error occurs:
+#import cgitb
+#cgitb.enable()
 
 # If you'd like to serve pages with UTF-8 instead of your default
 # locale charset, you can do so by uncommenting the following lines.