Refactor QueryableGraph and ThinNodeQueryableGraph to be independent interfaces, in preparation for further changes.

--
MOS_MIGRATED_REVID=126924789
diff --git a/src/main/java/com/google/devtools/build/skyframe/QueryableGraph.java b/src/main/java/com/google/devtools/build/skyframe/QueryableGraph.java
index ee09699..0419828 100644
--- a/src/main/java/com/google/devtools/build/skyframe/QueryableGraph.java
+++ b/src/main/java/com/google/devtools/build/skyframe/QueryableGraph.java
@@ -19,16 +19,11 @@
 
 import javax.annotation.Nullable;
 
-/**
- * A graph that exposes its entries and structure, for use by classes that must traverse it.
- */
+/** A graph that exposes its entries and structure, for use by classes that must traverse it. */
 @ThreadSafe
-public interface QueryableGraph extends ThinNodeQueryableGraph {
-  /**
-   * Returns the node with the given name, or {@code null} if the node does not exist.
-   */
+public interface QueryableGraph {
+  /** Returns the node with the given name, or {@code null} if the node does not exist. */
   @Nullable
-  @Override
   NodeEntry get(SkyKey key);
 
   /**
@@ -36,6 +31,5 @@
    * {@code keys}, {@code m.get(k).equals(e)} iff {@code get(k) == e} and {@code e != null}, and
    * {@code !m.containsKey(k)} iff {@code get(k) == null}.
    */
-  @Override
   Map<SkyKey, NodeEntry> getBatch(Iterable<SkyKey> keys);
 }