gnu: gtk: Replace librsvg with librsvg-bootstrap.

This is to use the same version of librsvg as used by the 'gtk+' package and
avoid propagation conflicts.

* gnu/packages/gtk.scm (guile-cairo)[inputs]: Remove librsvg.
[propagated-inputs]: Replace librsvg with librsvg-bootstrap.

gnu/packages/gtk.scm

@@ -1293,7 +1293,6 @@ (define-public gtk
            libcloudproviders            ;for cloud-providers support
            libjpeg-turbo
            libpng
-           librsvg
            libtiff
            python
            rest
@@ -1302,7 +1301,7 @@ (define-public gtk
      ;; Following dependencies are referenced in .pc files.
      (list cairo
            fontconfig
-           librsvg
+           librsvg-bootstrap
            glib
            graphene
            libepoxy