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

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MOS_MIGRATED_REVID=126924789
diff --git a/src/main/java/com/google/devtools/build/skyframe/EvaluableGraph.java b/src/main/java/com/google/devtools/build/skyframe/EvaluableGraph.java
index 7527146..b3d8bd0 100644
--- a/src/main/java/com/google/devtools/build/skyframe/EvaluableGraph.java
+++ b/src/main/java/com/google/devtools/build/skyframe/EvaluableGraph.java
@@ -22,7 +22,7 @@
  * single version of the graph.
  */
 @ThreadSafe
-interface EvaluableGraph extends QueryableGraph {
+interface EvaluableGraph extends QueryableGraph, DeletableGraph {
   /**
    * Like {@link QueryableGraph#getBatch}, except it creates a new node for each key not already
    * present in the graph. Thus, the returned map will have an entry for each key in {@code keys}.