various: do not use assert_se as a workaround in non-test code

This partially reverts 5332be60d3. I expect that
there is no practical difference, but it seems philosophically wrong to use
assert_se(), i.e. for the generation of the code in non-debug builds, just to
suppress a warning. We have _unused_ for that, use it.

I verified that we don't get warnings with clang and -DNDEBUG=1 with this patch.

src/shared/tpm2-util.c

@@ -4723,9 +4723,10 @@ static int tpm2_kdfe(
         if (!info)
                 return log_oom_debug();
 
-        void *end = mempcpy(mempcpy(stpcpy(info, label) + 1, context_u, context_u_size), context_v, context_v_size);
+        _unused_ void *end = mempcpy(mempcpy(stpcpy(info, label) + 1, context_u, context_u_size),
+                                     context_v, context_v_size);
         /* assert we copied exactly the right amount that we allocated */
-        assert_se(end > info && (uintptr_t) end - (uintptr_t) info == info_len);
+        assert(end > info && (uintptr_t) end - (uintptr_t) info == info_len);
 
         _cleanup_free_ void *buf = NULL;
         r = kdf_ss_derive(