Unify input prefetching

All prefetching now goes through AbstractSpawnStrategy's implementation of
SpawnExecutionPolicy. Make sure the sandbox runners also do this consistently.

PiperOrigin-RevId: 164836877
diff --git a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
index 4c7fa63..2475b2c 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
@@ -232,7 +232,7 @@
     }
 
     @Override
-    public void prefetchInputs(Iterable<ActionInput> inputs) throws IOException {
+    public void prefetchInputs() throws IOException {
       throw new UnsupportedOperationException();
     }