Merge branch 'hn/refs-test-cleanup'
A handful of tests that assumed implementation details of files
backend for refs have been cleaned up.
* hn/refs-test-cleanup:
t6001: avoid direct file system access
t6500: use "ls -1" to snapshot ref database state
t7064: use update-ref -d to remove upstream branch
t1410: mark test as REFFILES
t1405: mark test for 'git pack-refs' as REFFILES
t1405: use 'git reflog exists' to check reflog existence
t2402: use ref-store test helper to create broken symlink
t3320: use git-symbolic-ref rather than filesystem access
t6120: use git-update-ref rather than filesystem access
t1503: mark symlink test as REFFILES
t6050: use git-update-ref rather than filesystem access