Add support for @removed tag.

@removed tags can be applied to packages, classes, methods, fields
that were once public API, but later removed. Things annotated by
@removed cannot be used by outside developers. But applications compiled
against the old API where the @removed API were still public should
continue to work and we must not delete the @removed APIs from the
source. This fix makes sure of that.

BUG: b/11293324

Change-Id: Iab3a8bdcaa0cb0742501c33e29b8121bc169bf1b
diff --git a/src/com/google/doclava/NavTree.java b/src/com/google/doclava/NavTree.java
index e36babe..cc4f43f 100644
--- a/src/com/google/doclava/NavTree.java
+++ b/src/com/google/doclava/NavTree.java
@@ -64,7 +64,7 @@
 
     SortedMap<String, Object> sorted = new TreeMap<String, Object>();
     for (ClassInfo cl : classes) {
-      if (cl.isHidden()) {
+      if (cl.isHiddenOrRemoved()) {
         continue;
       }
       sorted.put(cl.qualifiedName(), cl);