local: build local provider conditionally
    
    Let's "get rid" of the local provider and only build it conditionally.
    
    The local provider is only used by our integration tests and those will
    be ran in the CI enabling the local provider.
    
    If someone, for some reason, still needs to use it,
    "--enable-local-provider" has been added as a configure option and the
    provider can be built using that (as done in our integration tests).
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3304
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>