Do not remove the demand on arguments without updating the result type

The CPR and termination information of a strictness signature depends on
the number arguments. If the latter is changed, e.g. in dmdAnalRHS, the
former needs to be adjusted.
postProcessUnsat should not remove CPR information

as it is still valid, as we did not change the number of arguments of
the demand signature.
CPR testcase: AnonLambda
Note [Recursion and nested cpr] and test case

the reason why we remove the converging flag of LoopBreakers is actually
non-obvious, and has little to do with the termination analysis per se.
Document that with an extensive note and guard it with two test cases.
More tracing in the demand analyser
Work in progress: nested-cpr.tex

A formal description of the nested CPR property (but the usefulness of
such is limited, it seems...)