Fix TCompLoop printing being stateful

[sim642]

Previously when using d_plaintype (or any other plain printing which includes the type) twice in a row on a recursive struct, the first output has TComp outside and TCompLoop on the fields:

TPtr(TComp(struct __pthread_internal_list,
              __prev : TPtr(TCompLoop(struct __pthread_internal_list, _, ), ),
              __next : TPtr(TCompLoop(struct __pthread_internal_list, _, ), ), ,
        ), )

Due to the statefulness of the plain printer, a second call with exactly the same type already has TCompLoop outside:

TPtr(TCompLoop(struct __pthread_internal_list, _, ), )

This is annoying for incremental analysis in Goblint, where messages will differ only in this aspect because the incremental run will skip over some earlier evaluation that made the first call, moving the first call with the different output to a different place. It shows spurious differences in messagesCompare.

By removing the compinfo after recursing, the plain printer becomes functionally pure, so all calls consistently print the first output from above.