removeRenderTarget(renderTarget) {
        if(!this.gl) return;

        let hasPlane = this.planes.find(plane => plane.type !== "PingPongPlane" && plane.target && plane.target.uuid === renderTarget.uuid);

        // loop through all planes that might use that render target and reset it
        for(let i = 0; i < this.planes.length; i++) {
            if(this.planes[i].target && this.planes[i].target.uuid === renderTarget.uuid) {
                this.planes[i].target = null;
            }
        }

        this.renderTargets = this.renderTargets.filter(element => element.uuid !== renderTarget.uuid);

        // update render target indexes
        for(let i = 0; i < this.renderTargets.length; i++) {
            this.renderTargets[i].index = i;
        }

        renderTarget = null;

        // clear the buffer to clean scene
        if(this.gl) this.clear();

        // we had at least a plane that was rendered in this render targets stack
        // re init stacks
        if(hasPlane) {
            this.scene.resetPlaneStacks();
        }

        // we've removed an object, keep Curtains class in sync with our renderer
        this.onSceneChange();
    }
Completely remove a RenderTarget element

     params:
     @renderTarget (RenderTarget object): the render target to remove
*