libbinder: eliminate Binder.cpp dependency on IShellCallback

Binder.cpp uses IShellCallback::asInterface to convert a Binder
to an IShellCallback, but the return value is not currently used.
This comments out that cast to eliminate the dependency on
IShellCallback, so we can build a minimal libbinder without it.

Bug: 224644083
Test: atest binderRpcTest
Change-Id: I209b1d2fd32cd9538c27aa263a6bf0a7e479fab1
diff --git a/libs/binder/Binder.cpp b/libs/binder/Binder.cpp
index b9a8ba9..532bacb 100644
--- a/libs/binder/Binder.cpp
+++ b/libs/binder/Binder.cpp
@@ -648,13 +648,14 @@
             for (int i = 0; i < argc && data.dataAvail() > 0; i++) {
                args.add(data.readString16());
             }
-            sp<IShellCallback> shellCallback = IShellCallback::asInterface(
-                    data.readStrongBinder());
+            sp<IBinder> shellCallbackBinder = data.readStrongBinder();
             sp<IResultReceiver> resultReceiver = IResultReceiver::asInterface(
                     data.readStrongBinder());
 
             // XXX can't add virtuals until binaries are updated.
-            //return shellCommand(in, out, err, args, resultReceiver);
+            // sp<IShellCallback> shellCallback = IShellCallback::asInterface(
+            //        shellCallbackBinder);
+            // return shellCommand(in, out, err, args, resultReceiver);
             (void)in;
             (void)out;
             (void)err;