tools: Fix RPM building without optional modules
tools: Fix RPM building without optional modules

When building without `build_optional` and `build_dashboard`, RPM build
failed because e. g. datadir/cockpit/dashboard/ did not exist. Don't
fail the `rm`s on missing files.

stefwalter/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mareklibra/cockpit,andreasn/cockpit,mareklibra/cockpit,martinpitt/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,deryni/cockpit,andreasn/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpituous/cockpit,garrett/cockpit,mvollmer/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,andreasn/cockpit,mvollmer/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,mvollmer/cockpit,deryni/cockpit,cockpituous/cockpit,andreasn/cockpit,stefwalter/cockpit,andreasn/cockpit,mvollmer/cockpit,deryni/cockpit,mareklibra/cockpit,cockpituous/cockpit,garrett/cockpit,stefwalter/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,garrett/cockpit,garrett/cockpit,deryni/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,martinpitt/cockpit,andreasn/cockpit,deryni/cockpit,mvollmer/cockpit