Make subclass inheritance more comfortable

remove same `copy` function

src/cameras/Camera.d.ts

@@ -31,8 +31,6 @@ export class Camera extends Object3D {
 
 	isCamera: true;
 
-	copy( source: Camera, recursive?: boolean ): this;
-
 	getWorldDirection( target: Vector3 ): Vector3;
 
 	updateMatrixWorld( force?: boolean ): void;

src/core/Object3D.d.ts

@@ -346,6 +346,6 @@ export class Object3D extends EventDispatcher {
 	 * @param object
 	 * @param recursive
 	 */
-	copy( source: Object3D, recursive?: boolean ): this;
+	copy( source: this, recursive?: boolean ): this;
 
 }

src/objects/Mesh.d.ts

@@ -24,6 +24,5 @@ export class Mesh extends Object3D {
 	setDrawMode( drawMode: TrianglesDrawModes ): void;
 	updateMorphTargets(): void;
 	raycast( raycaster: Raycaster, intersects: Intersection[] ): void;
-	copy( source: this, recursive?: boolean ): this;
 
 }

src/scenes/Scene.d.ts

@@ -26,7 +26,6 @@ export class Scene extends Object3D {
 	autoUpdate: boolean;
 	background: null | Color | Texture;
 
-	copy( source: this, recursive?: boolean ): this;
 	toJSON( meta?: any ): any;
 	dispose(): void;