Why:
* Protected variables were introduced to support temporary accounts
so that temporary users could be filtered based on their IP address.
* Filters that use protected variables are protected in order to
preserve privacy. This can't be undone.
* It is mistakenly possible to protect a filter that does not use
protected variables (T378553). We need a mechanism to fix these
mistakes.
What:
* Introduce a maintenance script that takes a filter ID and, if the
filter is protected, sets it to unprotected while maintaining any
other existing privacy levels.
Bug: T378551
Change-Id: I4dfe3970221397d5be5ea0697490d8c8e3726adf
