Fix errors caught by go vet in compliance package

`go test` implicitly runs `go vet` and fails the tests if vet
errors are found.  Fix all the issues found by vet.

Test: go test build/make/tools/compliance/...
Change-Id: If0684cf124ece4931af440008cd44a61c22de475
diff --git a/tools/compliance/policy/shareprivacyconflicts_test.go b/tools/compliance/policy/shareprivacyconflicts_test.go
index 2d2a1d0..069daa2 100644
--- a/tools/compliance/policy/shareprivacyconflicts_test.go
+++ b/tools/compliance/policy/shareprivacyconflicts_test.go
@@ -99,7 +99,7 @@
 			stderr := &bytes.Buffer{}
 			lg, err := toGraph(stderr, tt.roots, tt.edges)
 			if err != nil {
-				t.Errorf("unexpected test data error: got %w, want no error", err)
+				t.Errorf("unexpected test data error: got %s, want no error", err)
 				return
 			}
 			expectedConflicts := toConflictList(lg, tt.expectedConflicts)