Core: Exclude callbacks & deferred modules in the slim build as well

Core: Exclude callbacks & deferred modules in the slim build as well

So far, the slim build only excluded ajax & effects modules. As many web apps
right now rely on native Promises, often with a polyfill for legacy browsers,
deferred & callbacks modules are not that useful for sites that already exclude
ajax & effects modules.

This decreases the gzipped minified size of the slim module by 1760 bytes,
to 19706 bytes (below 20k!).

Closes gh-4553