drm/xe/guc: Remove duplicate source field

xe_hw_engine_snapshot.source save the information of where data copied
from. Because the 'source' field is already populated inside
'matched_node' ptr hanging off xe_devcoredump_snapshot, which happenned
either in guc_capture_extract_reglists or xe_engine_manual_capture, we
can remove this redundant copy of 'source' from xe_hw_engine_snapshot.

Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>

Changes from prior revs:
 v2:- Update commit message

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241107213841.436384-1-zhanjun.dong@intel.com