Drop tweak version component from CMake Policies

Since commit v2.8.2~105^2~2 (Teach CMake Policies about tweak version
component, 2010-04-23), cmPolicies has known how to handle a policy
introduced in a tweak version.  This was done back when we introduced
policies with the current development date version and later updated it
to the release version.  Now we always introduce policies using the next
expected release version and explicitly set the policy to test the NEW
behavior.

CMake Policies (or any other features) should never be introduced in a
tweak (bugfix) release, so drop the infrastructure that allows this.
Merge topic 'no-policy-tweak-version' into next

101057b5 Drop tweak version component from CMake Policies