Remove android system expat support.

Remove android system expat support.

Clean up the gyp/gn files by removing support for linking to the android
system expat. We don't intend to support this in future and the
android_src variable it depends on will be removed soon.

BUG=409851
Committed: https://crrev.com/4898820bd13a57512c5b714cf8cdebc8a698332c
Cr-Commit-Position: refs/heads/master@{#293843}

[Torne, 2014-09-08 10:57:55]

torne@chromium.org changed reviewers:
+ brettw@chromium.org

[Torne, 2014-09-08 10:57:55]

Brett, does the change to the GN file here look right?

[Torne, 2014-09-08 14:36:42]

torne@chromium.org changed reviewers:
+ primiano@chromium.org

[Primiano Tucci (use gerrit), 2014-09-08 14:46:16]

lgtm

[brettw, 2014-09-08 20:06:42]

lgtm

[Torne, 2014-09-08 20:26:27]

The CQ bit was checked by torne@chromium.org

[commit-bot: I haz the power, 2014-09-08 20:28:42]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/torne@chromium.org/550113003/1

[commit-bot: I haz the power, 2014-09-09 03:40:53]

Committed patchset #1 (id:1) as c8347ceeb49536801c45128ec1f1d44ee393efae

[commit-bot: I haz the power, 2014-09-10 03:50:01]

Patchset 1 (id:??) landed as
https://crrev.com/4898820bd13a57512c5b714cf8cdebc8a698332c
Cr-Commit-Position: refs/heads/master@{#293843}