bisect: no longer try to clean up left-over .git/head-name files

As per the code comment, the `.git/head-name` files were cleaned up for
backwards-compatibility: an old version of `git bisect` could have left
them behind.

Now, just how old would such a version be? As of 0f497e7 (Eliminate
confusing "won't bisect on seeked tree" failure, 2008-02-23), `git
bisect` does not write that file anymore. Which corresponds to Git
v1.5.4.4.

Even if the likelihood is non-nil that there might still be users out
there who use such an old version to start a bisection, but then decide
to continue bisecting with a current Git version, it is highly
improbable.

So let's remove that code, at long last.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

bisect.c

@@ -474,7 +474,6 @@ static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
 static GIT_PATH_FUNC(git_path_bisect_log, "BISECT_LOG")
 static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
 static GIT_PATH_FUNC(git_path_bisect_first_parent, "BISECT_FIRST_PARENT")
-static GIT_PATH_FUNC(git_path_head_name, "head-name")
 
 static void read_bisect_paths(struct strvec *array)
 {
@@ -1173,8 +1172,6 @@ int bisect_clean_state(void)
 	unlink_or_warn(git_path_bisect_run());
 	unlink_or_warn(git_path_bisect_terms());
 	unlink_or_warn(git_path_bisect_first_parent());
-	/* Cleanup head-name if it got left by an old version of git-bisect */
-	unlink_or_warn(git_path_head_name());
 	/*
 	 * Cleanup BISECT_START last to support the --no-checkout option
 	 * introduced in the commit 4796e823a.

t/t6030-bisect-porcelain.sh

@@ -990,7 +990,6 @@ test_expect_success 'git bisect reset cleans bisection state properly' '
 	test_path_is_missing ".git/BISECT_LOG" &&
 	test_path_is_missing ".git/BISECT_RUN" &&
 	test_path_is_missing ".git/BISECT_TERMS" &&
-	test_path_is_missing ".git/head-name" &&
 	test_path_is_missing ".git/BISECT_HEAD" &&
 	test_path_is_missing ".git/BISECT_START"
 '