Fix: Remove the duplicate parameter when generating the scaladoc.

[Dedelweiss]

When generating Scaladoc, a duplicate of the parameter appears at the beginning of each signature.
The solution here was to remove this line, as the parameter is already present in the argsSig value.

Before :

After :

I didn't do a test because I don't think there is one (or I couldn't find it). But if needed, a next PR or a next commit to add them can be done.

Fixes: #16647

[KacperFKorban]

Thanks for the fix. Looks good.

I didn't do a test because I don't think there is one (or I couldn't find it).

I think that we don't test extension signatures in scaladoc. (Though we probably should, since I'm 99% sure that this is a regression)