drm/i915: Remove the now obsolete 'i915_gem_check_olr()'

As there is no OLR to check, the check_olr() function is now a no-op and can be
removed.

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Tomas Elf <tomas.elf@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>