[depends] bump python27 to 2.7.14

[Rechi]

Description

• use expat version from depends instead of bundled version from python
• bump python to version 2.7.14
• some cosmetics

Motivation and Context

Bundled expat was bumped and now doesn't compile anymore on osx (not tested other platforms). I didn't want to fix that so just switched to use version from our depends.

How Has This Been Tested?

compiled depends for osx, ios, appletvos and android
runtime tested (including elementtree module) on osx

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the Code guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have added tests to cover my change
• All new and existing tests passed

[Rechi]

@wsnipex ping

[wsnipex]

lgtm