test: drop TEST_DATA_DIR, fold into get_testdata_dir()

Drop the TEST_DATA_DIR macro as this was using alloca() within a
function call which is allegedly unsafe. So add a "suffix" argument to
get_testdata_dir() instead and call that directly.

src/resolve/test-dns-packet.c

@@ -29,10 +29,9 @@
 #include "resolved-dns-rr.h"
 #include "string-util.h"
 #include "strv.h"
+#include "tests.h"
 #include "unaligned.h"
 
-#include "test-helper.h"
-
 #define HASH_KEY SD_ID128_MAKE(d3,1e,48,90,4b,fa,4c,fe,af,9d,d5,a1,d7,2e,8a,b1)
 
 static void verify_rr_copy(DnsResourceRecord *rr) {
@@ -117,7 +116,7 @@ int main(int argc, char **argv) {
                 N = argc - 1;
                 fnames = argv + 1;
         } else {
-                assert_se(glob(TEST_DATA_DIR("/test-resolve/*.pkts"), GLOB_NOSORT, NULL, &g) == 0);
+                assert_se(glob(get_testdata_dir("/test-resolve/*.pkts"), GLOB_NOSORT, NULL, &g) == 0);
                 N = g.gl_pathc;
                 fnames = g.gl_pathv;
         }