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>

buildscripts/rebrand-guard/compat-baseline.json

@@ -289,16 +289,6 @@
     "MINIO_IDENTITY_TLS_SKIP_VERIFY",
     "MINIO_IDENTITY_TLS_STS_EXPIRY",
     "MINIO_IDLE_TIMEOUT",
-    "MINIO_ILM_ACCESS_BINS",
-    "MINIO_ILM_ACCESS_BIN_WIDTH",
-    "MINIO_ILM_ACCESS_FLUSH",
-    "MINIO_ILM_ACCESS_MAX_SIZE",
-    "MINIO_ILM_ACCESS_MAX_TRACKED",
-    "MINIO_ILM_ACCESS_MIN_RESIDENCY",
-    "MINIO_ILM_ACCESS_POOLS",
-    "MINIO_ILM_ACCESS_PROMOTE_WATERMARK",
-    "MINIO_ILM_ACCESS_TIERING",
-    "MINIO_ILM_ACCESS_WORKERS",
     "MINIO_ILM_EXPIRATION_WORKERS",
     "MINIO_ILM_TRANSITION_WORKERS",
     "MINIO_INTERFACE",
@@ -745,7 +735,6 @@
     "/idp/ldap/policy/{operation}",
     "/idp/openid/list-access-keys-bulk",
     "/ilm",
-    "/ilm/access",
     "/import-bucket-metadata",
     "/import-iam",
     "/import-iam-v2",
@@ -915,6 +904,7 @@
     ".minio.sys/config/config.json",
     ".minio.sys/config/hello.txt",
     ".minio.sys/config/iam/${username}/identity.json",
+    ".minio.sys/config/ilm/access",
     ".minio.sys/format.json",
     ".minio.sys/multipart",
     ".minio.sys/multipart/bucket/object/uploads.json",