graphics/librsvg2-rust: update to 2.54.5

• Drop USE_GNOME=gnomeprefix to support DOCS option via conditional --disable-gtk-doc and remove unsupported --with-html-dir --with-gconf-source (configure warning)

Changes: https://gitlab.gnome.org/GNOME/librsvg/-/blob/2.54.5/NEWS
Reported by: GitLab (notify releases)