cockpit.spec: Drop obsolete shell override.json on RHEL
cockpit.spec: Drop obsolete shell override.json on RHEL

The "linguas" option in the manifest got dropped a long time ago, and
the language switcher works fine in RHEL 7/8.

Closes #11906

garrett/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,mvollmer/cockpit,mvollmer/cockpit,deryni/cockpit,cockpituous/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,cockpituous/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit