collate/build: do not use println in tests

Change-Id: I4f50430a35b009618c4762c74c418919dc54cdb1
Reviewed-on: https://go-review.googlesource.com/c/text/+/634495
Reviewed-by: Sean Liao <[email protected]>
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Junyang Shao <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: alexandear

collate/build/contract_test.go

@@ -247,7 +247,6 @@ func TestPrintContractionTrieSet(t *testing.T) {
 	print(&testdata, buf, "test")
 	if contractTrieOutput != buf.String() {
 		t.Errorf("output differs; found\n%s", buf.String())
-		println(string(buf.Bytes()))
 	}
 }