Remove `amp-live-list-sorting` experiment flag

[erwinmombay]

Remove once #5396 requirements are fully implemented

[ampprojectbot]

This issue seems to be in Pending Triage for awhile. @erwinmombay Please triage this to an appropriate milestone.

[ampprojectbot]

This issue seems to be in Pending Triage for awhile. @erwinmombay Please triage this to an appropriate milestone.

[ampprojectbot]

This issue seems to be in Pending Triage for awhile. @erwinmombay Please triage this to an appropriate milestone.