t9001: remove excessive GIT_SEND_EMAIL_NOTTY=1

This was added by 3ece9bf (send-email: clear the $message_id after
validation, 2023-05-17) for no apparent reason, as this is required only
in cases when git's stdin is (must be) redirected, which isn't the case
here.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ossilator

t/t9001-send-email.sh

@@ -592,7 +592,6 @@ test_expect_success $PREREQ 'clear message-id before parsing a new message' '
 	clean_fake_sendmail &&
 	echo true | write_script my-hooks/sendemail-validate &&
 	test_config core.hooksPath my-hooks &&
-	GIT_SEND_EMAIL_NOTTY=1 \
 	git send-email --validate --to=recipient@example.com \
 		--smtp-server="$(pwd)/fake.sendmail" \
 		$patches $threaded_patches &&