Inline the ResourceDeclaration struct in TaskResource

Before the commit 92d5bcc, attributes
of `ResourceDeclaration` belong to `TaskResource`.

This avoids generated JSON structures to contain the useless
`ResourceDeclaration` attribute.

pkg/apis/pipeline/v1alpha1/task_types.go

@@ -117,7 +117,7 @@ type Inputs struct {
 // path to the volume mounted containing this Resource as an input (e.g.
 // an input Resource named `workspace` will be mounted at `/workspace`).
 type TaskResource struct {
-	ResourceDeclaration
+	ResourceDeclaration `json:",inline"`
 	// +optional
 	OutputImageDir string `json:"outputImageDir,omitempty"`
 }