Stop granting permission to report_off_body to keystore2

The report_off_body permission of the "keystore2" class only guarded the
Binder API IKeystoreMaintenance#onDeviceOffBody() served by keystore2.
That API is being removed because it is unused
(https://r.android.com/2974277).  Therefore, stop granting the
report_off_body permission.

Don't actually remove the permission from private/access_vectors.  That
would break the build because it's referenced by rules in prebuilts/.
However, document the access vectors that are known to be unused.

Bug: 289849354
Test: atest CtsKeystoreTestCases
Change-Id: I344a1a8ad1dc12217b414899994397d5e62bd771
diff --git a/private/access_vectors b/private/access_vectors
index 32d73dd..60ec0ae 100644
--- a/private/access_vectors
+++ b/private/access_vectors
@@ -692,7 +692,7 @@
 	list
 }
 
-class keystore_key
+class keystore_key # No longer used
 {
 	get_state
 	get
@@ -727,11 +727,11 @@
 	get_attestation_key
 	get_auth_token
 	get_last_auth_time
-	get_state
+	get_state # No longer used
 	list
 	lock
 	pull_metrics
-	report_off_body
+	report_off_body # No longer used
 	reset
 	unlock
 }