6874521: Remove @note tags

[Alan Bateman]

Joe mentioned to me that there are a couple of javadoc warnings due to 
non-standard tags that weren't removed when the nio2 code was pushed 
into jdk7. These can be trivially removed. Martin also pointed out the 
@see references in java.nio.file.FileRef a few weeks ago. These can be 
removed for now and re-added once those classes are finalized.

The webrev is here:
 http://cr.openjdk.java.net/~alanb/6874521/webrev.00/

Thanks,
Alan.