RFR: JDK-8062661 Do not perform X11 checks in configure when X11 is not needed

[Magnus Ihse Bursie]

Configure has been testing for X11 even though it was not needed (on 
macosx and windows). This never caused any failures (since we ignore any 
results indicating that X11 is missing), but it looks silly.

Bug: https://bugs.openjdk.java.net/browse/JDK-8062661
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8062661-dont-check-X11-if-not-needed/webrev.01

/Magnus