RFR: 8214532,Update RFC 2459 references in javadoc to RFC 5280

[Seán Coffey]

Some doc edits to update RFC 2459 to 5280. I've updated the relevant 
section numbers where necessary.

No edits to Java SE specification docs. I've taken the opportunity to 
put a space in some "RFCxxxx" references also as it seems to be 
preferred approach. I've removed a paragraph in 
src/java.base/share/classes/sun/security/x509/X509CertImpl.java also 
which seemed obsolete.

I'd like to push this doc edit to JDK 12.

http://cr.openjdk.java.net/~coffeys/webrev.8214532/webrev/

-- 
Regards,
Sean.