ixgbevf: remove Tx hang detection

Removed Tx hang detection mechanism from ixgbevf.
This mechanism has no affect and can cause false alarm messages in some
cases. Especially when VF Tx rate limit is turned on.

The same mechanism was removed recently from igbvf.

Signed-off-by: Lior Levy <lior.levy@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>