[docs] Parameter doc section has unnecessary leading `:`

[jameslamb]

If you run ?pkgnet::InheritanceReport, you'll see a section like this:

And the same on the pkgdown site (https://uptake.github.io/pkgnet/reference/InheritanceReporter.html)

Since the parameter names are nicely being put in their own left-aligned heading and then the description is indented over, I think we should remove the leading :. It looks out of place.

Not sure if this is affecting other documentation in the project, but whoever picks up this issue should look at all of it.