Fixes <https://bugs.gnu.org/40806>.
Previously the xorg-server package specified in the configuration was ignored
entirely in xorg-configuration->file. This had the effect that while the X
program of the configured package would be executed, the modules of the
configured package would be ignored in favor of the default xorg-server
package's modules. This fixes that.
* gnu/services/xorg.scm (xorg-configuration->file): honor
xorg-configuration-server.
