Fix incorrect getType signature/implementation in doc.

The method is missing the Uri parameter and the implementation is
both inefficient and unnecessary. It is documented as fine to
return null in getType.

Change-Id: I78c83918916ca5ef28172e544d9ddc9c3695444d

docs/html/training/sync-adapters/creating-stub-provider.jd

@@ -85,11 +85,11 @@ public class StubProvider extends ContentProvider {
         return true;
     }
     /*
-     * Return an empty String for MIME type
+     * Return no type for MIME type
      */
     @Override
-    public String getType() {
-        return new String();
+    public String getType(Uri uri) {
+        return null;
     }
     /*
      * query() always returns no results