fix: Remove LooseVersion

[hoxbro]

Fixes #109

kernel_version is no longer used, so we can remove the import of LooseVersion.

[peytondmurray]

Thanks for this, I was just running into this on #64. I'm not sure what the intent was in defining kernel_version; I guess for compatibility we could use packaging.version.Version in case someone is making use of it, although I'd be surprised if it was.

[hoxbro]

It was added in #36 to be compatible with ipykernel 6 and was removed in #93.

Replacing it with packaging.version.Version will still break if people use it, as it no longer works with string equality check. So, I don't think it is worth keeping.