[PATCH] do not set GIT_TEST_MAINT_SCHEDULER where it does not matter

[Junio C Hamano <gitster@pobox.com>]

31345d55 (maintenance: extract platform-specific scheduling,
2020-11-24) added code to t/test-lib.sh for everybody to set
GIT_TEST_MAINT_SCHEDULER to a "safe" value and instructed the test
writers to set the variable locally when their test wants to check
the scheduler integration.

But it did so without "export GIT_TEST_MAINT_SCHEDULER", so the
setting does not seem to have any effect anyway.  Instead of setting
it to a "safe" value, just unset it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * t7900 (maintenance) uses many tests that does one-shot export of
   the variable, and one test that sets the value to its safe
   "failure" value and exports it at the end.

   t9210 (scaler) sets up a safe fake scheduler and exports it
   before doing any of its tests.

   Nobody else that includes t/test-lib.sh mentions this variable.

 t/test-lib.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git c/t/test-lib.sh w/t/test-lib.sh
index c8af8dab79..48345864f4 100644
--- c/t/test-lib.sh
+++ w/t/test-lib.sh
@@ -1959,9 +1959,9 @@ test_lazy_prereq DEFAULT_REPO_FORMAT '
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.
-# Tests that verify the scheduler integration must set this locally
-# to avoid errors.
-GIT_TEST_MAINT_SCHEDULER="none:exit 1"
+# Tests that verify the scheduler integration must set and
+# export this variable locally.
+sane_unset GIT_TEST_MAINT_SCHEDULER
 
 # Does this platform support `git fsmonitor--daemon`
 #