t-example-decorate: remove test messages

t-example-decorate: remove test messages

The test_msg() calls only repeat information already present in test
descriptions and check definitions, which are shown automatically if
the checks fail.  Remove the redundant messages to simplify the tests
and their output.  Here it is with all of them failing before:

 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:18
 # when adding a brand-new object, NULL should be returned
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:21
 # when adding a brand-new object, NULL should be returned
 not ok 1 - Add 2 objects, one with a non-NULL decoration and one with a NULL decoration.
 # check "ret == &vars->decoration_a" failed at t/unit-tests/t-example-decorate.c:29
 # when readding an already existing object, existing decoration should be returned
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:32
 # when readding an already existing object, existing decoration should be returned
 not ok 2 - When re-adding an already existing object, the old decoration is returned.
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:40
 # lookup should return added declaration
 # check "ret == &vars->decoration_b" failed at t/unit-tests/t-example-decorate.c:43
 # lookup should return added declaration
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:46
 # lookup for unknown object should return NULL
 not ok 3 - Lookup returns the added declarations, or NULL if the object was never added.
 # check "objects_noticed == 2" failed at t/unit-tests/t-example-decorate.c:58
 #    left: 1
 #   right: 2
 # should have 2 objects
 not ok 4 - The user can also loop through all entries.
 1..4

... and here with the patch applied:

 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:18
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:20
 not ok 1 - Add 2 objects, one with a non-NULL decoration and one with a NULL decoration.
 # check "ret == &vars->decoration_a" failed at t/unit-tests/t-example-decorate.c:27
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:29
 not ok 2 - When re-adding an already existing object, the old decoration is returned.
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:36
 # check "ret == &vars->decoration_b" failed at t/unit-tests/t-example-decorate.c:38
 # check "ret == NULL" failed at t/unit-tests/t-example-decorate.c:40
 not ok 3 - Lookup returns the added declarations, or NULL if the object was never added.
 # check "objects_noticed == 2" failed at t/unit-tests/t-example-decorate.c:51
 #    left: 1
 #   right: 2
 not ok 4 - The user can also loop through all entries.
 1..4

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>