drm/i915/gem: Remove duplicated call to ops->pread

Between

commit ae30af84
Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date:   Tue Mar 23 16:50:00 2021 +0100

    drm/i915: Disable userptr pread/pwrite support.

and

commit 0049b688
Author: Matthew Auld <matthew.auld@intel.com>
Date:   Thu Nov 5 15:49:33 2020 +0000

    drm/i915/gem: Allow backends to override pread implementation

this accidentally landed twice.

Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210616090350.828696-1-daniel.vetter@ffwll.ch