*.sh: drop useless use of "env"

In a bourne shell script, "VAR=VAL command" is sufficient to run
'command' with environment variable VAR set to value VAL without
affecting the environment of the shell itself; there is no need
to say "env VAR=VAL command".

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

t/t1020-subdirectory.sh

@@ -148,7 +148,7 @@ test_expect_success 'GIT_PREFIX for built-ins' '
 	(
 		cd dir &&
 		printf "change" >two &&
-		env GIT_EXTERNAL_DIFF=./diff git diff >../actual
+		GIT_EXTERNAL_DIFF=./diff git diff >../actual
 		git checkout -- two
 	) &&
 	test_cmp expect actual

t/t9001-send-email.sh

@@ -409,7 +409,7 @@ test_expect_success $PREREQ 'Valid In-Reply-To when prompting' '
 	(echo "From Example <from@example.com>"
 	 echo "To Example <to@example.com>"
 	 echo ""
-	) | env GIT_SEND_EMAIL_NOTTY=1 git send-email \
+	) | GIT_SEND_EMAIL_NOTTY=1 git send-email \
 		--smtp-server="$(pwd)/fake.sendmail" \
 		$patches 2>errors &&
 	! grep "^In-Reply-To: < *>" msgtxt1