### Please describe the problem.

After once embedding credentials into a S3 remote, there’s no way to un-embed them.

### What steps will reproduce the problem?

1. Add a S3 remote with `embedcreds=yes`.
1. Try to set `embedcreds=no`.
1. `git annex sync` here, and in some other clone.
1. Check `git annex info my-s3-remote` for the other clone. Credentials are still embedded.

### What version of git-annex are you using? On what operating system?

6.20170101 on NixOS 16.09 (stable).

### Please provide any additional information below.

[[!format sh """
% g annex info test2 | grep '^creds'
creds: embedded in git repository (gpg encrypted)

% g annex enableremote test2 embedcreds=no
enableremote test2 (encryption update) (to gpg keys: 134164FA6FAFE075) ok
(recording state in git...)

% g annex info test2 | grep '^creds'
creds: embedded in git repository (gpg encrypted)

%
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes, it’s awesome! Thank you!
