[cleanup] Remove duplicate netext entries
[cleanup] Remove duplicate netext entries

with https://gerrit.wikimedia.org/r/#/c/pywikibot/core/+/606671/
netext xdict has a fallback to wikipedia entries. Duplicate
codes may be removed.

Change-Id: I06b0084390ce6b3497e5d29b0113af6b447439ea

wikimedia/pywikibot-core,wikimedia/pywikibot-core