mktag tests: don't redirect stderr to a file needlessly

Remove the redirection of stderr to "message" in the valid tag
test. This pattern seems to have been copy/pasted from the failure
case in 446c6faec6 (New tests and en-passant modifications to mktag.,
2006-07-29).

While I'm at it do the same for the "replace" tests. The tag creation
I'm changing here seems to have been copy/pasted from the "mktag"
tests to those tests in cc400f5011 (mktag: call
"check_sha1_signature" with the replacement sha1, 2009-01-23).

Nobody examines the contents of the resulting "message" file, so the
net result is that error messages cannot be seen in "sh t3800-mktag.sh
-v" output.

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

t/t3800-mktag.sh

@@ -222,7 +222,7 @@ EOF
 
 test_expect_success \
     'allow empty tag email' \
-    'git mktag <tag.sig >.git/refs/tags/mytag 2>message'
+    'git mktag <tag.sig >.git/refs/tags/mytag'
 
 ############################################################
 # 16. disallow spaces in tag email
@@ -350,7 +350,7 @@ EOF
 
 test_expect_success \
     'create valid tag' \
-    'git mktag <tag.sig >.git/refs/tags/mytag 2>message'
+    'git mktag <tag.sig >.git/refs/tags/mytag'
 
 ############################################################
 # 25. check mytag

t/t6050-replace.sh

@@ -129,7 +129,7 @@ tagger T A Gger <> 0 +0000
 EOF
 
 test_expect_success 'tag replaced commit' '
-     git mktag <tag.sig >.git/refs/tags/mytag 2>message
+     git mktag <tag.sig >.git/refs/tags/mytag
 '
 
 test_expect_success '"git fsck" works' '