Using SelectAttr in conjunction with PUT is duplicative and problematic

This issue will depend upon the resolution of CAMP-36 but, if people agree we should use JSON Patch for fine-grained updates, there really isn't any need to support PUTs that use the SelectAttr parameter. Furthermore, supporting SelectAttr in the context of PUT is a mess implementation-wise. There are a bunch of tricky corner cases in which you have to make sure that request body doesn't contain any attributes that aren't selected, check for "implicit deletes" in which the user selects an attribute but don't supply a value in the body, etc.