jsonrpc: revert switch to the simplejson module

This reverts commit 58553451547fe70958c01585f58d50c8ed75493b.

It is too late to have a new dependency in the stable branch.

Change-Id: I4d165b4698dd30de27bc46c7157585bd0477c70a
Bug-Url: https://bugzilla.redhat.com/1155146
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35347
Reviewed-by: Dan Kenigsberg <danken@redhat.com>