Revert "http_connection: Allow empty json objects"

This reverts commit 02e01b51.

This commit is being reverted because it causes login failures on
Firefox browsers.  This commit originally was added with the idea that
it did not fix anything on upstream, but made some peoples forks better.

It appears to have broken some upstream things, so the right thing to do
is to revert it until those breakages can be understood.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I04de84fca1a8de657f6941653f2a3e595ee725d5