Rename "rollback index slot" to "rollback index location".

This is because the word slot is already used in the context of
A/B. Less confusing this way.

Bug: 33100927
Test: New unit tests and all unit tests pass.
Test: Manually tested on UEFI based bootloader.

Change-Id: Ic611b02dc18e7dd9f14c2c87b247be3cd8f4aaf2
diff --git a/test/fake_avb_ops.h b/test/fake_avb_ops.h
index 76d452d..6aa8be4 100644
--- a/test/fake_avb_ops.h
+++ b/test/fake_avb_ops.h
@@ -83,10 +83,10 @@
                                          size_t public_key_metadata_length,
                                          bool* out_key_is_trusted);
 
-  AvbIOResult read_rollback_index(AvbOps* ops, size_t rollback_index_slot,
+  AvbIOResult read_rollback_index(AvbOps* ops, size_t rollback_index_location,
                                   uint64_t* out_rollback_index);
 
-  AvbIOResult write_rollback_index(AvbOps* ops, size_t rollback_index_slot,
+  AvbIOResult write_rollback_index(AvbOps* ops, size_t rollback_index_location,
                                    uint64_t rollback_index);
 
   AvbIOResult read_is_device_unlocked(AvbOps* ops,