graphics/librsvg2-rust: Update to 2.45.7

rsvg-view is no longer provided by librsvg [1]. Drop the workaround
that was there to avoid a dependency loop with gtk3.

[1] https://people.gnome.org/~federico/blog/removing-rsvg-view.html

Changes: https://download.gnome.org/sources/librsvg/2.45/librsvg-2.45.7.news