Use aaload instead of getfield for accessing elements in a list.

Previously, the code used `getfield` to access elements in a list. While
this is not incorrect, this change made the code more consistent with
`functools.xml`, which uses `aaload`.

Author: khatchad

com.ibm.wala.cast.python.ml/data/tensorflow.xml

@@ -1048,7 +1048,8 @@
         <!-- https://www.tensorflow.org/versions/r2.9/api_docs/python/tf/data/Dataset#choose_from_datasets -->
         <method name="do" descriptor="()LRoot;" numArgs="3" paramNames="datasets choice_dataset stop_on_empty_dataset">
           <!-- Return the first one in the list. -->
-          <getfield class="Llist" field="0" fieldType="Ltensorflow/data/Dataset" ref="datasets" def="x" />
+          <constant name="l" type="int" value="0" />
+          <aaload index="l" type="Ltensorflow/data/Dataset" ref="datasets" def="x" />
           <return value="x" />
         </method>
       </class>
@@ -1108,7 +1109,8 @@
     <package name="tensorflow/distribute/run">
       <class name="run" allocatable="true">
         <method name="do" descriptor="()LRoot;" numArgs="3">
-          <getfield class="LRoot" field="0" fieldType="LRoot" ref="arg2" def="x" />
+          <constant name="l" type="int" value="0" />
+          <aaload index="l" type="LRoot" ref="arg2" def="x" />
           <call class="LRoot" name="do" descriptor="()LRoot;" type="virtual" arg0="arg1" arg1="x" numArgs="2" def="v" />
           <return value="v" />
         </method>