fix(gatsby): Fix various small DEV_SSR bugs exposed in development_runtime tests

[KyleAMathews]

Backport of #29720 to v2

[ascorbic]

@KyleAMathews These seem to be real test failures. Could you take a look?

[KyleAMathews]

Gah can't reproduce locally. It's a strange error that I'm not sure how my changes would cause:

Your callback function returned a promise that never resolved.

The callback function was:

win => {
    if (!win.___apiHandler) {
      win.___apiHandler = _apiHandler.default.bind(win);
    }

    return _apiHandler.waitForAPI.call(win, api).then(() => subject);
  }

Will add some debugging code I guess to see what api isn't returning.

[KyleAMathews]

Ok, turned out I had some left code in assuming DEV_SSR was at 100%