Fix #299: Use xoroshiro assembly routine for x86
In #294 (closed), we implemented the xoroshiro update function as an assembly routine instead of a VOP. However, it couldn't be enabled there and still used the VOP.
This actually enables the use of the assembly routine and removes the old VOP code.
To get the CI to work, we also needed to modify .gitlab-ci.yml to use the xoroshiro-assembly snapshot builds which include the assembly routine already in the core. This is needed to be able to use the routine.
Edited by Raymond Toy