drm/i915: Remove defunct GTT tracepoints

The tracepoints are now entirely synonymous with binding and unbinding the
VMA (and the tracepoints there).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170215084357.19977-18-chris@chris-wilson.co.uk