Fix guard for UseMockKeyStorageForTesting

https://codereview.chromium.org/2086123003/
introduced the possibility to either use Libsecret or KWallet.

I'm updating a guard that I forgot to reflect the change.

BUG=602624

Review-Url: https://codereview.chromium.org/2104943002
Cr-Commit-Position: refs/heads/master@{#402469}
1 file changed