Remove HTTP pipelining support.

It's been a couple years since anyone worked on it, and there
are no plans to enable it by default.

Cached pipelining-related server information will automatically
be cleared when server information is next saved, so there are
no issues on that front.

BUG=364557
R=asvitkine@chromium.org, eroman@chromium.org, grt@chromium.org, sky@chromium.org, willchan@chromium.org, zea@chromium.org

Review URL: https://codereview.chromium.org/275953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272903 0039d316-1c4b-4281-b951-d872f2087c98
94 files changed