Removed linking libraries to init_script_test_helper

The `init_script_test_helper` binary does not require any libraries.
The libraries `libpromises.la` and `libtest.la` were previously added
through the `LDADD` variable in the top of Makefile.am.

Ticket: CFE-2780
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

tests/unit/Makefile.am

@@ -399,6 +399,7 @@ check_PROGRAMS += nfs_test
 nfs_test_SOURCES = nfs_test.c
 nfs_test_LDADD = ../../libpromises/libpromises.la libtest.la
 
+init_script_test_helper_LDADD =
 init_script_test_helper_SOURCES = init_script_test_helper.c
 init_script_test.sh: init_script_test_helper
 CLEANFILES += init_script_test_helper