Pagination: absence of params means unlimited

It remains true that if `limit` is 0, then empty results
are expected, but absence of the `PaginationParameter` field
is used by Gitaly to mean no pagination.

In particular comments about breaking change for clients in
bb607763822c were just wrong.
4 jobs for !76 with topic/default/no-pagination in 1 minute and 33 seconds (queued for 6 seconds)
latest detached
Status Name Job ID Coverage
  Main
passed tests-current #244868

00:01:04

100.0%
 
  Compat
passed check-sdist #244869

00:00:48

passed tests-hg-default #244871

00:00:28

100.0%
passed tests-hg-stable #244870

00:00:26

100.0%