Fix API doc building errors due to incorrect parameter names.
Fix API doc building errors due to incorrect parameter names.

A change made in the upcoming 2.5.7 release included the addition of a
new related link for the review request resource. The implementatino of
`get_related_links()` accepted a `review_request` positional argument,
instead of an `obj` keyword argument, which ended up breaking doc
building.

This change renames the argument to `obj` in order to fix this. No other
behavior has changed.

Testing Done:
Built the docs successfully (along with another upcoming change).

Reviewed at https://reviews.reviewboard.org/r/8467/

sgallagher/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,brennie/reviewboard,sgallagher/reviewboard,davidt/reviewboard,davidt/reviewboard,chipx86/reviewboard,davidt/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,brennie/reviewboard,sgallagher/reviewboard,chipx86/reviewboard,brennie/reviewboard,sgallagher/reviewboard,davidt/reviewboard,chipx86/reviewboard,brennie/reviewboard