Drop the global permission "shareDashboards"

Users can share some of their dashboards to others. That requires the special global permission "shareDashboards".

There's no functional need for removing this permission to a user. Anybody should be able to share. People are free to not "follow" these dashboards.

Moreover in the context of organizations, the concept of global groups is being replaced by organization groups. As a consequence permissions, except "system administrator" status, are scoped to organizations (administer quality gates, administer quality profiles, manage members, ...). That does not make sense for sharing of dashboards.

As a consequence the ability to remove the permission of sharing can be dropped.