Makes a minor modification to allow compilation by Vala 0.17.2; closes #5453.
Makes a minor modification to allow compilation by Vala 0.17.2; closes #5453.

(Due to a binding change, Gtk.TreeStore's remove() now requires a 'ref' argument here.)
h4ck3rm1k3/shotwell,ritchiewilson/shotwell,polymeris/shotwell,polymeris/shotwell,jimbonator/shotwell,damianmoore/shotwell,abrauchli/shotwell,polymeris/shotwell,jimbonator/shotwell,ritchiewilson/shotwell,ritchiewilson/shotwell,abrauchli/shotwell,jimbonator/shotwell,h4ck3rm1k3/shotwell,damianmoore/shotwell,h4ck3rm1k3/shotwell,abrauchli/shotwell,damianmoore/shotwell