chore: drop test on Node 14/16

[JounQin]

I was going to enable https://github.com/ota-meshi/prettier-plugin-jsdoc-type at #729, but found out it's incompatible with Node 14/16.

[Green00101]

Hi, I’m interested in working on this issue. Could you assign it to me if it’s still available?

[BPScott]

We won't assign this to an external person. Dropping support for these old node versions is a breaking change. That will be handled by repo maintainers.

[Green00101]

I see, thanks for the reply.