put back localhost check for localdev

[erwinmombay]

@rsimha-amp do you remember why you removed that line?

[rsimha]

This was part of what @lannka suggested in the original issue. Let me dig in some more.

[rsimha]

Turns out the localhost check doesn't always work, and so, @lannka wanted it gone in lieu of always applying the prod config to local builds. See #8008 (comment)

In any case, since others are complaining that ads don't load without the localhost check, I'm going to approve this and take a closer look into what else we can do.

[rsimha]

For posterity, see #11588 for the PR that removed the localhost check

[lannka]

@erwinmombay @rsimha-amp do you recall what was the test pages got broken?

[rsimha]

@lannka the ads in http://localhost:8000/examples/ads.amp.html were 404ing without the localhost check

[lannka]

All ads broke because removing the localhost check makes isLocalDev false. hence all ads start to load 3p bootstrap frame from production with a wrong RTV path.

Let's discuss the solution on this thread: #12054