tests: use 'test_must_be_empty' instead of 'test_cmp <empty> <out>'

[git] / t / t5100 / patch0016--no-inbody-headers

---
diff --git a/foo b/foo
index e69de29..d95f3ad 100644
--- a/foo
+++ b/foo
@@ -0,0 +1 @@
+content