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

@@ -118,9 +118,8 @@ func TestKindSorter(t *testing.T) {
 			head: &util.SimpleHead{Kind: "StatefulSet"},
 		},
 		{
-			name:    "w",
-			content: "",
-			head:    &util.SimpleHead{Kind: "APIService"},
+			name: "w",
+			head: &util.SimpleHead{Kind: "APIService"},
 		},
 	}