Drop Node 16 support

[barjin]

Node 16 has been EoL for over two years.

After officially dropping Node 16 support, we could switch axios for the native fetch implementation, slimming down both the Node dependency installs and the browser bundle sizes (related to #812 )

Blocking #814 (maybe we can just stop testing for Node 16 for now?)

[B4nan]

I would just drop it from CI

[barjin]

Dropped Node 16 from CI in #814 . This issue is IMO still valid (see original description, e.g. usage of fetch, dropping dynamic imports of crypto for Webcrypto from #782 etc.).

Let's wait with these changes for 3.0, I suppose. At the same time, we now won't know if anything breaks for Node 16, so any PR can be breaking and we won't know.