Revert "WIP: test manual pruning of landing log"

This reverts commit 1214e0c479e2fa21ab91b864a222e4a872af1d54.
Arcyd: fetch special refs when fetching repos

Make it easier to cutover between repositories by fetching special refs
every time arcyd fetches a remote repository.  This removes the need for
the special command 'fetch-special', cutting over now simply means
stopping one instance and starting another.

Update acceptance tests to do no special cutover steps.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
Remove 'arcyd fetch-special' command

This command is no longer needed, remove it.  Arcyd now fetches the
special refs automatically.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh