Bug#703715: workaround makes it worse

[Daniel Pocock <daniel@pocock.com.au>]

I tried the workaround from the Ubuntu bug:

i915.i915_enable_rc6=0

After rebooting, I notice that the screen flashes at me from time to
time, and the errors are regularly appearing in dmesg, gdm login screen
broken, etc

[  164.522266] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer
elapsed... GPU hung
[  164.522272] [drm] capturing error event; look for more information in
/debug/dri/0/i915_error_state


I've now removed the workaround as it appears to make the problems worse