build-sys: Removed unused variable from configure.ac
build-sys: Removed unused variable from configure.ac

LIBGLUSTER_LIBS is emptied before gluster is enabled/disabled, but nothing
else sets/uses this variable, so it can be removed.

jfehlig/libvirt,agx/libvirt,shugaoye/libvirt,crobinso/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,agx/libvirt,fabianfreyer/libvirt,elmarco/libvirt,shugaoye/libvirt,olafhering/libvirt,zippy2/libvirt,rlaager/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,eskultety/libvirt,jardasgit/libvirt,jardasgit/libvirt,agx/libvirt,taget/libvirt,elmarco/libvirt,shugaoye/libvirt,jardasgit/libvirt,andreabolognani/libvirt,zippy2/libvirt,taget/libvirt,crobinso/libvirt,datto/libvirt,agx/libvirt,jardasgit/libvirt,libvirt/libvirt,rlaager/libvirt,eskultety/libvirt,VenkatDatta/libvirt,agx/libvirt,fabianfreyer/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,eskultety/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,libvirt/libvirt,libvirt/libvirt,eskultety/libvirt,datto/libvirt,jfehlig/libvirt,andreabolognani/libvirt,elmarco/libvirt,olafhering/libvirt,taget/libvirt,VenkatDatta/libvirt,olafhering/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,nertpinx/libvirt,nertpinx/libvirt,rlaager/libvirt,taget/libvirt,elmarco/libvirt,zippy2/libvirt,crobinso/libvirt,elmarco/libvirt,libvirt/libvirt,jfehlig/libvirt,crobinso/libvirt,rlaager/libvirt,jardasgit/libvirt,rlaager/libvirt,nertpinx/libvirt,olafhering/libvirt,eskultety/libvirt,andreabolognani/libvirt,datto/libvirt,jfehlig/libvirt,taget/libvirt,zippy2/libvirt,datto/libvirt