fpicker: cleanup async requests, dung out comments.

Change-Id: I016145d315ae1c4b5376e43583e2546a2b7f7b07
(cherry picked from commit acc0fcd96c940e42da27bb58ba1c89ae5de5a5b8)
Reviewed-on: https://gerrit.libreoffice.org/6736
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>