Revert "provider/manual: return hardware characteristics"

Reverts juju/juju#536

PR 536 is blocking CI, because tests fail for arch=386 and ppcel as seen in this bug: https://bugs.launchpad.net/juju-core/+bug/1358768

Environ.go line 474 appears to be where things fall down, when running go test with GOARCH=386.  

I don't have time to actually fix the problem, so just reverting the PR so we can unblock CI.