gnu: Remove librsvg-bootstrap.

librsvg is already a staging-level package, and the next version will no
longer bundle its dependencies, so we might as well drop it early.

* gnu/packages/gnome.scm (librsvg-bootstrap): Remove variable.
* gnu/packages/bittorrent.scm (deluge)[native-inputs]: Replace
LIBRSVG-BOOTSTRAP with LIBRSVG.
* gnu/packages/emacs.scm (emacs)[inputs]: Likewise.
* gnu/packages/gtk.scm (gtk+-2)[propagated-inputs]: Likewise.
* gnu/packages/gtk.scm (gtk+)[propagated-inputs]: Likewise.

gnu/packages/emacs.scm

@@ -289,7 +289,7 @@
            libpng
            zlib
            (if (target-x86-64?)
-               librsvg-bootstrap
+               librsvg
                librsvg-2.40)
            libxpm
            libxml2