remove `engines` field from package.json

[bgrins]

As per https://docs.npmjs.com/cli/v9/configuring-npm/package-json#engines

And, like with dependencies, if you don't specify the version (or if you specify "*" as the version), then any version of node will do.

So this section is unnecessary https://github.com/bgrins/TinyColor/blob/8707554b556fcaedcd1904765e3204feacd4fcac/npm/package.json#L17-L19