Cleanup: remove the namespace-level nodoc annotations from Extension API

Cleanup: remove the namespace-level nodoc annotations from Extension API
schemas.  They're unnecessary (controlled by the presence, or lack thereof, of
an HTML file documenting the API) and I keep on seeing code reviews of
cargo-culted APIs that add it.

R=rockot@chromium.org

Committed: https://crrev.com/b735be2e5de50ec5a973be5662aa7415c96c77ad
Cr-Commit-Position: refs/heads/master@{#307068}

[not at google - send to devlin, 2014-12-05 19:20:26]

(and I checked to make sure there aren't HTML files added for these already, so,
it's a no-op)

[Ken Rockot(use gerrit already), 2014-12-05 19:25:58]

lgtm

[not at google - send to devlin, 2014-12-05 19:26:26]

The CQ bit was checked by kalman@chromium.org

[commit-bot: I haz the power, 2014-12-05 19:27:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/754693004/1

[commit-bot: I haz the power, 2014-12-05 20:13:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-05 20:14:11]

Patchset 1 (id:??) landed as
https://crrev.com/b735be2e5de50ec5a973be5662aa7415c96c77ad
Cr-Commit-Position: refs/heads/master@{#307068}