[MD Settings] Add a menu option to clear a cached credit card.

This only applies to credit cards that were imported from Google
Payments and saved locally. Does not delete the credit card info from
the Google Payments servers.

BUG=622174
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2092323002
Cr-Commit-Position: refs/heads/master@{#402336}
5 files changed