[cleanup] Remove disfunctional versionnumber
[cleanup] Remove disfunctional versionnumber

- versionnumber is deprecated for 5 years and disfunctional.
  It returns 34 instead of 35 for the current release but
  would return 1023 for a mw '2.23.4-wmf.5' which is weird.
  It was introduced in compat to compare versions as an int.

Change-Id: Iaec5b758883285f0c37542f6b23ac6982225187e

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core