Prevent putting the same information twice in documentation

[bew]

Extracted from L3MON4D3/LuaSnip#1006

This comes from a slight annoyance of duplicated information for no reason.

With a simple snippet without explicit description, the doc looks like:

You can see we have modeline repeated twice in the doc popup
(and even 4 times if we count the completion popup and what I wrote / the inserted completion)

I would like to at least remove the docstring when it is the same as the trigger/name of the snippet.

Here is a simulation of the result I'd like to have:

👉 I'd even argue that when the snippet name is the same as the trigger (which is the default when the name isn't specified when defining a snippet), we could remove the name, or replace it with something else 👀

@L3MON4D3 mentioned we could just compare the name/trigger with the docstring and not display it if it's the same

[L3MON4D3]

Actually, if we're at this, maybe the trigger shouldn't even be displayed in the doc-window again since it's already in the list on the left?

[saadparwaiz1]

We just need to make the relevant changes in the get_documentation function. What's the exact behaviour would you guys prefer?