remove per account cpu statsd metrics

These haven't proven to be very useful, and they add a lot of graphite
load.

Change-Id: I5b23dc41c51e2d7d081b0d02edd1a10a6499a31e
Reviewed-on: https://gerrit.instructure.com/42969
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>