More tests that are marked as "ref-files only" have been updated to
improve test coverage of reftable backend.
* ps/ref-tests-update-even-more:
t7003: ensure filter-branch prunes reflogs with the reftable backend
t2011: exercise D/F conflicts with HEAD with the reftable backend
t1405: remove unneeded cleanup step
t1404: make D/F conflict tests compatible with reftable backend
t1400: exercise reflog with gaps with reftable backend
t0410: convert tests to use DEFAULT_REPO_FORMAT prereq
t: move tests exercising the "files" backend