rx: Remove the unused packet skew code

rx: Remove the unused packet skew code

We don't (and haven't, since the release of OpenAFS) use the packet
skew calculations for anything. However, maintaining them requires
taking locks in some critical parts of the transmission code path.
For both speed, and maintainability, reasons remove the skew code
from the tree - it's in git if we ever want to go back to it.

Change-Id: Idc6dc80fb06ca959ad02a85f2c536a94ca3d5c02
Reviewed-on: http://gerrit.openafs.org/7004
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>