nyxt.asd: Remove unused nyxt/build-rpm and nyxt/gtk-application-rpm.
nyxt.asd: Remove unused nyxt/build-rpm and nyxt/gtk-application-rpm.

They are superseded by the linux-packaging library.  We don't provide RPMs for
now, but adding support for them is a trivial addition to the package building
.asd.

jmercouris/NeXT,jmercouris/NeXT