Stop using third_party\python_26 for many tests.

Migrate testserver.py from using embedded python in third_party\python_26 to
the python version installed on the system.

Kill many python_26 references.

It reduces the amount of data that needs to be transfered for Windows swarm
slaves.

The remaining uses of third_party\python_26 are:
1. chrome_frame.
2. pyauto needs the python SDK. As such, it needs a "known" python installation.
3. gn.

R=phajdan.jr@chromium.org,rsleevi@chromium.org
BUG=98636
BUG=321703
TEST=

Review URL: https://codereview.chromium.org/74253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238989 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238989