love.audio.play(source) is a duplicate of source:play(), and so on.
I would assume that users who know about the Source methods would want to use source:play() etc., due to the concise syntax and consistency with other Source operations.
For users who don't know about the Source methods, I think that the duplicated functions in love.audio could be misleading. While it reduces the learning curve for some basic Source operations due to the familiar syntax, other common Source operations (such as looping) would require the user to learn about Source methods anyway, and if the user has controlled sources using the love.audio functions before, looking for Source methods might not be obvious.
If these functions were removed, I'd also suggest to consider appending "All" to the name of the appropriate love.audio functions (such as love.audio.pause becoming love.audio.pauseAll) to better describe their functionality.