Skip index cleanup if autovacuum did not do any work

On a server with a very frequent xid wraparound I can see that the
anti-wraparound vacuum is finished very quickly with the heap, yet it still
scans all the indexes, which causes it to still have to read a lot of data,
which takes a considerable amount of time.

I dove into the code a bit and as far as I can tell, all the time spent for
doing this is is in lazy_cleanup_index.

For the very specific use case of all-frozen, basically read-only tables,
would it be ok to skip the lazy_cleanup_index call? As we are sure we did
not touch the heap or the index, I'd say a cleanup may not be necessary.

For this very specific usecase I would like to discuss whether or not this
is
a sane and/or good idea.

regards,

Feike