tests: fix test-casefolding.t output for branchcache
This belongs with
7d63398fbfd1. I assume that the failure to read is OK,
because there is similar output in test-convert-svn-encoding.t.
setdiscovery: drop '_setupsample' usage in '_takequicksample'
For '_takefullsample' we can just retrieve the list of head directly and
ignore the rest of the complex return values. This was the last call to the
infamous '_updatesample' function.