filechooserentry: unselect text when unfocused

There's no gain in keeping text selected while entry is
unfocused other than confusing users which (misguided by
the strong selection color) think the entry is focused
and so when start typing to edit the text an unexpected
search dialog appears.

Fixes #326
Fixes #665
7 jobs for gtk3_fix_chooser_entry_selection in 15 minutes and 47 seconds (queued for 2 seconds)