Remove spurious field in kind sorter test

The test never reads the manifest type's "content" field, so there's
no reason to populate it explicitly with its zero value.

pkg/tiller/kind_sorter_test.go

@@ -119,7 +119,6 @@ func TestKindSorter(t *testing.T) {
 		},
 		{
 			name: "w",
-			content: "",
 			head: &util.SimpleHead{Kind: "APIService"},
 		},
 	}