Revert "Add String TypedTransfer::transferId() which returns null by default."

This reverts commit 36ad6ce.

Author: nedtwigg

durian-swt/src/main/java/com/diffplug/common/swt/dnd/TypedTransfer.java

@@ -23,11 +23,6 @@
 
 /** A strongly-typed custom transfer type. */
 public abstract class TypedTransfer<T> extends ByteArrayTransfer {
-	/** The transfer id. */
-	public @Nullable String transferId() {
-		return null;
-	}
-
 	public abstract T getValue(DropTargetEvent e);
 
 	public abstract void setValue(DragSourceEvent e, T value);