compiler: don't extract common exports

[josephjclark]

Short Description

There's a very gnarly bit of compiler code called preloadAdaptorExports which tries to work out the list of valid exports from an adaptor.

We've had a lot of trouble around this historically - it doesn't actually work terrible well, and relies on some ropey, poorly tested code in describe-adaptor

The problem right now is that the list of exports for an adaptor is very generous. We basically list every export listed in the d.ts (regardless of how or where it's exported). And for some reason we also list everything exported from common, regardless of whether it's actually exported from the adaptor. Frankly I forget what this is all about.

Now this is a problem when we have multiple adaptors, a la collections, because the compiler things that both http and collections export fn, so it'll try to import it from both packages. Resulting in all kinds of trouble.

My solution is the lowest effort, lowest risk thing I can see: only work out the exports for index.d.ts and adaptor.ts, because those two files are all that really matter for job code.

Now we're cheating a bit on the adaptors.d.ts thing, it's not a generic solution and makes an assumption about adaptor structure. But it's a fair one. And working out the exports properly, even with typescript, is actually really hard.

One day, when we re-write describe-package, we'll have a much more robust and generic solution for this sort of thing. But for now, I'll settle for this.

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