test-lib tests: remove dead GIT_TEST_FRAMEWORK_SELFTEST variable
Stop setting the GIT_TEST_FRAMEWORK_SELFTEST variable. This was originally needed
back in
4231d1ba99 (t0000: do not get self-test disrupted by
environment warnings, 2018-09-20).
It hasn't been needed since I deleted the relevant code in test-lib.sh
in
c0eedbc009 (test-lib: remove check_var_migration, 2021-02-09), I
just didn't notice that it was set here.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>