Remove unused PatchType N_WAY

This was the older `diff --cc` style output, which wasn't very useful
when reviewing a merge commit.  We plan to do merge reviews again
in the near future by comparing the result of the merge against the
automated machine performed merge, making it even more obvious what
the human author changed.

Change-Id: I2355b50a88f798526ed72b5e36ad84298d81f991
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/Patch.java

@@ -136,29 +136,7 @@ public final class Patch {
      * the only information it can display is the old and new file content
      * hashes.
      */
-    BINARY('B'),
-
-    /**
-     * Difference of three or more textual contents.
-     *
-     * <p>
-     * Git can produce an n-way unified diff, showing how a merge conflict was
-     * resolved when two or more conflicting branches were merged together in a
-     * single merge commit.
-     *
-     * <p>
-     * This type of patch can only appear if there are two or more
-     * {@link PatchSetAncestor} entities for the same parent {@link PatchSet},
-     * as that denotes that the patch set is a merge commit.
-     *
-     * <p>
-     * Gerrit can only render an N_WAY file in a PatchScreen.Unified view, as it
-     * does not have code to split the n-way unified diff into multiple edit
-     * lists, one per pre-image. However, a logical way to display this format
-     * would be an n-way table, with n+1 columns displayed (n pre-images, +1
-     * post-image).
-     */
-    N_WAY('N');
+    BINARY('B');
 
     private final char code;