dataflash viewer filter list shows formats

When using the dataflash log viewer's filter feature (click on the column header row), if we scroll down in the list of options, down at the bottom are a bunch of format strings which I don't think should be there.


Reproduce the issue in Mission Planner's dataflash log viewer by opening a column-header filter and scrolling through its option list. Trace the filter list's source and ensure the unwanted format strings no longer appear; verify that valid filter options still work.

Written by the indexing model from the issue text.