Merge branch 'js/test-initial-branch-override-cleanup'

Many tests that used to need GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
mechanism to force "git" to use 'master' as the default name for
the initial branch no longer need it; the use of the mechanism from
them have been removed.

* js/test-initial-branch-override-cleanup:
  tests: set GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME only when needed

diff --cc t/t1400-update-ref.sh
Simple merge

diff --cc t/t5310-pack-bitmaps.sh
Simple merge