Remove DeveloperError in release build

[pjcozzi]

A quick test shows that we can drop ~100 KB from the ~1.2 MB minified Cesium.js if we remove the developer errors. I expect this will also reduce the size of AMD-based apps quite a bit. Although it is not significant compared to the graphics assets downloaded, it is significant for the initial load.

We can expect a minor performance win too; however, I no longer see defined on any profiles.

Here's a few options for implementing this:

• Use a RegEx to replace the DeveloperError strings with an empty string or even the filename and line number.
• Surround the DeveloperError if blocks with a #ifdef and use the JS minifier preprocessor. Be careful not to include side-effects, e.g., i++, inside the #ifdef block. This will reduce the size even more and may improve performance. In order for the default build to work, the preprocessor commands would need to be commented out so the browsers don't choke on them.
• Inject if (false) { /* ... */ } blocks at build time and let the minifier remove them. However, this is dangerous for side-effects since it's not obvious to the original developer.

I'd probably go with (1) and then maybe (2).

[pjcozzi]

Although outside the scope of this issue, if we use the preprocessor, there are other things we can exclude from release builds like debugShowBoundingVolume.

[pjcozzi]

The infrastructure for this was added in #1296. We still need to add pragmas to most places.