Remove Python 2.5 support from WebKit

Remove Python 2.5 support from WebKit
https://bugs.webkit.org/show_bug.cgi?id=71593

Reviewed by Adam Barth.

Just removing support from this one core file.
I'll commit the rest of the (large) change once we've
gone 24 hours and seen that no bots have exploded.
We can roll out this one change if we break bots
and then roll in the rest once those bots are fixed.

* Scripts/webkitpy/common/system/executive.py:
(Executive.cpu_count):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105931 268f45cc-cd09-0410-ab3c-d52691b4dbfc