t/t9001-send-email.sh: Remove needless PROG=* assignment

Remove the PROG=* assignment from t9001-send-email.sh. It's been there
since v1.4.0-rc1~30 when the test was originally added, but only tests
that source annotate-tests.sh need it, it was seemingly introduced to
this test via copy/paste coding.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -8,7 +8,6 @@ if ! test_have_prereq PERL; then
 	test_done
 fi
 
-PROG='git send-email'
 test_expect_success \
     'prepare reference tree' \
     'echo "1A quick brown fox jumps over the" >file &&