revert: remove access-frequency ILM tiering (#60)

Reverse the first-parent diff of a3df317ae0,
including the feature branch compatibility and mover follow-up fixes.
Retain the independent multi-pool correctness fixes from #178 and migrate
their shared test fixture away from access-tier code.

Tolerate retired ILM keys and XML, read old v9 statistics while writing v8,
and document migration without moving objects or rewriting their metadata.
Include regression coverage using a historical scanner/writer v9 fixture.

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/server-main.go

@@ -501,7 +501,6 @@ func initAllSubsystems(ctx context.Context) {
 	globalTierConfigMgr = NewTierConfigMgr()
 
 	globalTransitionState = newTransitionState(GlobalContext)
-	globalAccessTierState = newAccessTierState(GlobalContext)
 	globalSiteResyncMetrics = newSiteResyncMetrics(GlobalContext)
 }
 
@@ -1070,10 +1069,6 @@ func serverMain(ctx *cli.Context) {
 		bootstrapTrace("globalTransitionState.Init", func() {
 			globalTransitionState.Init(newObject)
 		})
-		bootstrapTrace("globalAccessTierState.Init", func() {
-			globalAccessTierState.Init(newObject)
-			go globalAccessTracker.run(GlobalContext, newObject)
-		})
 
 		go func() {
 			// Initialize transition tier configuration manager