Revert "setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR"

This reverts d95138e6 (setup: set env $GIT_WORK_TREE when work tree
is set, like $GIT_DIR, 2015-06-26).

It has caused three regression reports so far.

  http://article.gmane.org/gmane.comp.version-control.git/281608
  http://article.gmane.org/gmane.comp.version-control.git/281979
  http://article.gmane.org/gmane.comp.version-control.git/282691

All of them are about spawning git subprocesses, where the new
presence of GIT_WORK_TREE either changes command behaviour (git-init
or git-clone), or how repo/worktree is detected (from aliases), with
or without $GIT_DIR.

The original bug will be re-fixed another way.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

environment.c

@@ -211,8 +211,6 @@ void set_git_work_tree(const char *new_work_tree)
 	}
 	git_work_tree_initialized = 1;
 	work_tree = xstrdup(real_path(new_work_tree));
-	if (setenv(GIT_WORK_TREE_ENVIRONMENT, work_tree, 1))
-		die("could not set GIT_WORK_TREE to '%s'", work_tree);
 }
 
 const char *get_git_work_tree(void)

t/t0002-gitfile.sh

@@ -99,7 +99,7 @@ test_expect_success 'check rev-list' '
 	test "$SHA" = "$(git rev-list HEAD)"
 '
 
-test_expect_success 'setup_git_dir twice in subdir' '
+test_expect_failure 'setup_git_dir twice in subdir' '
 	git init sgd &&
 	(
 		cd sgd &&