Remove margin for selected files summary

The selected files summary shown in the multiselect header has a margin
to align it with the names of the files in the contents of the file
list. However, on very narrow screens, and depending on the verbosity of
the language, the summary can overlap with the actions when the
selection contains files and folders. To try to mitigate this, besides
showing only the icons for the actions, the summary margin is removed
too in very narrow screens.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>