remove dist-import in node & layers

[WenheLI]

This is about tensorflow/tfjs-node#289.
This pr removes dist-importing in tfjs-node and tfjs-layers.
The rest of the removing will be at a separate PR.

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This change is 

[WenheLI]

@dsmilkov - Hey Daniel, it seems that the CI will run changes separately based on different folders they are in.
Am I right about this?
As I need to import tslint in the root folder, but the test in react-native does not have the change about tslint in the root folder.

[dsmilkov]

Hi, yes, CI runs separately for each folder, however because you are touching the global tslint.json, which is shared across all projects, the CI will run the lint job across all folders. So you will need to fix the dist imports across all projects.