[Smart Lock, UI] Change cancel button to Never, save prompt.

Currently if save prompt was triggered via Credential Management API,
the cancel button says "No Thanks" and do not blacklist the site.

After this patch the button will say "Never" and id user presses the
button, it will blacklist the site.

BUG=528980

Review URL: https://codereview.chromium.org/1402463004

Cr-Original-Commit-Position: refs/heads/master@{#354001}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 8fbacd4a393a056fe76e4cb1accf13ecfc03858d

ios/grit_whitelist.txt

@@ -706,7 +706,6 @@ IDS_PASSWORDS_EXCEPTIONS_TAB_TITLE
 IDS_PASSWORDS_SHOW_PASSWORDS_TAB_TITLE
 IDS_PASSWORD_MANAGER_BLACKLIST_BUTTON
 IDS_PASSWORD_MANAGER_SAVE_BUTTON
-IDS_PASSWORD_MANAGER_SAVE_PASSWORD_SMART_LOCK_NO_THANKS_BUTTON
 IDS_PASSWORD_MANAGER_SMART_LOCK
 IDS_PASSWORD_MANAGER_SMART_LOCK_PAGE
 IDS_PAST_TIME_TODAY