CountHook is an implementation of terraform.Hook which is used to
calculate how many resources were added, changed, or destroyed during an
apply. This hook was previously injected in the local backend code,
which means that the apply command code has no access to these counts.
This commit moves the CountHook code into the command package, and
removes an unused instance of the hook in the plan code path. The goal
here is moving UI code into the command package.
Alisdair McDiarmid