spec: Fix obsoleting of c-dashboard also for Fedora
spec: Fix obsoleting of c-dashboard also for Fedora

It was in condition for RHEL only.
Don't use 'Provides' as [1] states:
```
If a package supersedes/replaces an existing package without being a sufficiently
compatible replacement as defined above, use only the Obsoletes: line from the above example.
```

Related to https://bugzilla.redhat.com/show_bug.cgi?id=1911825

[1] https://docs.fedoraproject.org/en-US/packaging-guidelines/#renaming-or-replacing-existing-packages
cockpit-project/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit