iwl3945: remove plcp check

Patch fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=654599

Many users report very low speed problem on 3945 devices,
this patch fixes problem, but only for some of them.

For unknown reason, sometimes after hw scanning, device is not able
to receive frames at high rate. Since plcp health check may request
hw scan to "reset radio", performance problem start to be observable
after update kernel to .35, where plcp check was introduced.

Bug reporter confirmed that removing plcp check fixed problem for him.

Reported-and-tested-by: SilvioTO <silviotoya@yahoo.it>
Cc: stable@kernel.org  # 2.6.35+
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>