t: convert tests to not access reflog via the filesystem
Some of our tests reach directly into the filesystem in order to both read or modify the reflog, which will break once we have a second reference backend in our codebase that stores reflogs differently. Refactor these tests to either use git-reflog(1) or the ref-store test helper. Note that the refactoring to use git-reflog(1) also requires us to adapt our expectations in some cases where we previously verified the exact on-disk log entries. This seems like an acceptable tradeoff though to ensure that different backends have the same user-visible behaviour as any user would typically use git-reflog(1) anyway to access the logs. Any backend-specific verification of the written on-disk format should be implemented in a separate, backend-specific test. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>