Merge topic 'simplify-removed-policies'

ff9bc7291a cmPolicies: Remove now-unused GetRequiredPolicyError method
659d8bd430 cmPolicies: Remove now-unused REQUIRED_IF_USED and REQUIRED_ALWAYS states
58a90857f0 cmPolicies: Simplify representation of removed policies
dade821948 cmPolicies: Reduce boilerplate in policy table entries
453916dfae cmPolicies: Add missing license notice
9a28b0654f cmGeneratorExpressionNode: Clarify constant in unreachable code path

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Acked-by: Craig Scott <craig.scott@crascit.com>
Merge-request: !9993