gs-history-dialog: Remove this widget

Since removing the details grid from `GsDetailsPage`, it is no longer
used. It was not fully implemented by backends (only the PackageKit
backend ever calls `gs_app_add_history()`, and that’s in a trivial way)
and hence was not useful.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
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