Those assertions are not necessary anymore, since the commonizer is not
expected to produce any new "actuals" per given expect.
The IDE is supposed to analyze leaf source sets against the original
platform libraries.
1. Drop CirClassifierId
2. Specialized classes for each kind of types (classes, TAs, type parameters, flexible types).
3. TypeCommonizer now returns commonized type. In case of TAs this could be a completely new type
describing expect class or a new TA with the different underlying type.
sebastian.sellmair