[OpenJDK 2D-Dev] RFR: 8178457: Remove link to 2D guide from Line2D javadoc

[Phil Race]

A small javadoc change to link to a different more stable source
of information on the Java 2D coord. system.

Bug : https://bugs.openjdk.java.net/browse/JDK-8178457

Patch:
--- a/src/java.desktop/share/classes/java/awt/geom/Line2D.java
+++ b/src/java.desktop/share/classes/java/awt/geom/Line2D.java
@@ -35,8 +35,7 @@
   * default coordinate system called <i>user space</i> in which the y-axis
   * values increase downward and x-axis values increase to the right.  For
   * more information on the user space coordinate system, see the
- * <a href="{@docRoot}/../technotes/guides/2d/spec/j2d-intro.html">
- * Coordinate Systems</a> section of the Java 2D Programmer's Guide.
+ * {@link java.awt.Graphics2D} class documentation.
   * <p>
   * This class is only the abstract superclass for all objects that
   * store a 2D line segment.

-phil.