python-pexpect: drop old version recipe

Drop old version recipe of python-pexpect and use the one in oe-core
which version is 3.3 now. And according to release notes of version 3.0,
"The new major version number doesn’t indicate any deliberate API
incompatibility."

Ref:
http://pexpect.readthedocs.org/en/stable/history.html



Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>