remove constants.js size

[hugomrdias]

Any chance we can reduce the size of the constants.js file ?

/cc @vmx @jacobheun

[vmx]

js-multicodec could be used, which is a dependency on a lot of things that use js-multihash anyway.

[hugomrdias]

that would be perfect what about the codes and sizes ?

[vmx]

The codes are part of js-multicodec, the sizes are not (and i also don't find the sizes generally useful. Without checking the code, I would imagine we could just get rid of the default sizes).