opam: few improvements
opam: few improvements

- Remove version line. It previously seemed necessary to manage
co-developed packages, but seems not to be required anymore.
- Merge install commands into build section. These commands didn’t
actually do any installing, just built files needed only for
installation. We thus avoid opam-lint warning 27.
- Use %{name}% instead of hard-coding the package name.

solvuu/solvuu_build,solvuu/solvuu-build