`spack gc` removes build deps of explicitly installed specs, but somehow
if you take one of the specs that `spack gc` would remove, and feed it
to `spack uninstall /<hash>` by hash, it complains about all the
dependents that still rely on it.
This resolves the inconsistency by only following run/link type deps in
spack uninstall.
That way you can finally do `spack uninstall cmake` without having to
remove all packages built with cmake.
09eb86e077