Plotly.react always redraw if a config option is provided

Running tests in `plot_api_test.js` result in `Test plot api @noCIdep Plotly.react can redraw "airfoil" with no changes as a noop (svg mocks) FAILED`.

The culprit is in PR https://github.com/plotly/plotly.js/pull/3090 which introduces new private attributes into `_context`. Because `diffConfig` does not ignore those, `Plotly.react` always redraw.