drm/xe/doc: Remove KEEP_ACTIVE feature
The KEEP_ACTIVE feature is being reverted, update documentation.
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260106191051.2866538-6-niranjana.vishwanathapura@intel.com