I noticed that I had the same issue when the nupkg file was 33 MB, 5 MB more than the max size of 28.5 Mb. Deleting the unnecessary references hardly reduced the size by 1 Kb each. But when I removed the PDF that is in the Documents folder (the one that comes with REF template) my nupkg file size reduced from 33 Mb all the way down to 999Kb.
So I think that would be a better and more effective way to fix this issue, should you run into it.