Revert "settings: Check if xhr response text include ':' or not."
Revert "settings: Check if xhr response text include ':' or not."

This reverts commit dd406e87e.  Whatever awkward error message might
have motivated that change, we can fix in a more targeted way when we
see it again.  This version would delete the potentially-informative
context the caller provided in `response` -- even just "Failed" --
based on whether an error message happened to contain a colon
somewhere in it, which is sure to end up feeling unpredictable.

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