t4200: drop irrelevant code
While setting up an unresolved merge for `git rerere`, we run `git
rev-parse` and `git fmt-merge-msg` to create a variable `$fifth` and a
commit-message file `msg`, which we then never actually use. This has
been like that since these tests were added in
672d1b789b ("rerere:
migrate to parse-options API", 2010-08-05). This does exercise `git
rev-parse` and `git fmt-merge-msg`, but doesn't contribute to testing
`git rerere`. Drop these lines.
Reported-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>