Should references to the appendix be removed from a camera ready paper?
As a general rule, papers should be self-contained. A reference to an appendix would violate this rule if the paper is distributed without the appendix.

Instead, a best practice is to have a reference to an extended version of the paper that includes the appendix:


  The proof of this result is provided in [1].
  
  
  A. Nonymous: How to write a paper (extended version). 2018. Available online at http://arxiv.org/some/url
  


The extended version would then have the same sentence, but with a reference to the appendix:


  The proof of this result is provided in the appendix.