fix(lsp): remove BufEnter event on linting

[rgruyters]

When in use, linting will also be triggered when viewing lsp signature help (or lsp hover)

If you enter a hover- or signature help window, markdownlint triggers warninging within the LSP window. This is very annoying and shouldn't be triggered.

Here is a screenshot what happens when entering a LSP window.

[ccjmne]

Hmm, that's pretty smart. It's something that's been bothering me as well!
But then I suppose that you won't quite get diagnostics as you purposefully open a buffer whose linting you care for... Not until you enter and leave insert mode or write your buffer to a file, is that correct?

It may be better to identify somehow that the buffer you just entered is actually a pop-up one, and only disable these.

[ccjmne]

We could consider skipping the linting for read-only buffers. It works nicely, but may be undesirable in some cases.

[rgruyters]

Hmm, that's pretty smart. It's something that's been bothering me as well! But then I suppose that you won't quite get diagnostics as you purposefully open a buffer whose linting you care for... Not until you enter and leave insert mode or write your buffer to a file, is that correct?

Yes that is correct.

It may be better to identify somehow that the buffer you just entered is actually a pop-up one, and only disable these.

That would be much better solution, but I didn't know how.

[rgruyters]

I will close this PR, in favor for #1202