Correct the description for getKeyCharacteristics

The description should note that keystore-enforced tags are not to be
returned. This is done so that the keymint implementation doesn't have
to bother keeping track of tags it's not repsonsible for dealing with.

Bug: 186685601
Test: none (it's just a comment change)
Change-Id: I3ff94201c262a5071d271b150dbbf21888d678aa
diff --git a/security/keymint/aidl/android/hardware/security/keymint/IKeyMintDevice.aidl b/security/keymint/aidl/android/hardware/security/keymint/IKeyMintDevice.aidl
index 9cc795d..5b0b303 100644
--- a/security/keymint/aidl/android/hardware/security/keymint/IKeyMintDevice.aidl
+++ b/security/keymint/aidl/android/hardware/security/keymint/IKeyMintDevice.aidl
@@ -805,9 +805,10 @@
     byte[] convertStorageKeyToEphemeral(in byte[] storageKeyBlob);
 
     /**
-     * Returns parameters associated with the provided key. This should match the
-     * KeyCharacteristics present in the KeyCreationResult returned by generateKey(),
-     * importKey(), or importWrappedKey().
+     * Returns KeyMint-enforced parameters associated with the provided key. The returned tags are
+     * a subset of KeyCharacteristics found in the KeyCreationResult returned by generateKey(),
+     * importKey(), or importWrappedKey(). The returned value is a subset, as it does not include
+     * any Keystore-enforced parameters.
      *
      * @param keyBlob The opaque descriptor returned by generateKey, importKey or importWrappedKey.
      *