Remove redundant render context lookup in Renderer::doRender()

Problem/Motivation

Renderer::doRender() receives the render context as a required argument, but still retrieves and checks it again.

Background

The same lookup was already removed from the access-denied path in #2511330: Deprecate RendererInterface::render()'s sole $is_root_call parameter.

This is a followup to #2511330: Deprecate RendererInterface::render()'s sole $is_root_call parameter.

Proposed resolution

Remove the remaining redundant lookup and check.

Remaining tasks

Review.

User interface changes

None.

Introduced terminology

None.

API changes

None.

Data model changes

None.

Release notes snippet

n/a

Original report

Followup to #2511330: Deprecate RendererInterface::render()'s sole $is_root_call parameter.

Renderer::doRender() receives the render context as a required argument, but still retrieves and checks it again.

The same lookup was already removed from the access-denied path in #2511330: Deprecate RendererInterface::render()'s sole $is_root_call parameter.

Remove the remaining redundant lookup and check.