drm/i915/gt: remove stray declaration of intel_gt_release_all()

When intel_gt_release_all() was removed from the code in commit
e8995055 ("drm/i915: do not clean GT table on error path"), its
declaration in the header file remained.  Remove it.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240813140618.387553-1-luciano.coelho@intel.com