[deps] Remove pycparser dependency
[deps] Remove pycparser dependency

'pycparser!=2.14' was introduced as security dependency for
cryptography needed by requests[security] for older Python versions
due to a bug with release 2.14.

It is not necessary for Python newer than 2.7.8 and
can be removed because 2.20 was published.

Change-Id: I5f588e6091b7642fde0b2dbb4df30527df6a2af2

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