drm/xe/mcr: Remove unused xe_gt_mcr_steering_info_to_dss_id()

drm/xe/mcr: Remove unused xe_gt_mcr_steering_info_to_dss_id()

The function xe_gt_mcr_steering_info_to_dss_id() has had no callers
since commit fa597710be6e ("drm/xe/guc: Cache DSS info when creating
capture register list") which removed the only call site in
xe_guc_capture.c. Remove the dead function and its declaration.

No functional change.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20260422155025.3660484-1-shuicheng.lin@intel.com
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>