and remove now unused IsFileFilter method.

Change-Id: I6b4559fdf6442b6baa869b2949142f8fc8c52f30
Reviewed-on: https://gerrit.libreoffice.org/9223Reviewed-by: Maxim Monastirsky <momonasmon@gmail.com>
Tested-by: Maxim Monastirsky <momonasmon@gmail.com>