Update Spack package to build GridKit without dependencies by default

[nkoukpaizan]

#186 sets up the GridKit CMake to GridKit without dependencies by default
This should be reflected in the Spack package as well. See https://github.com/nkoukpaizan/spack/blob/Gridkit-package-dev%2Benzyme--upgrade/var/spack/repos/builtin/packages/gridkit/package.py#L22

[pelesh]

I believe the current Spack package will still build correctly with SUNDIALS always enabled, no?

[nkoukpaizan]

I believe the current Spack package will still build correctly with SUNDIALS always enabled, no?

Yes.