Remove some obsolete comments from ada-varobj.c

I noticed a few spots in ada-varobj.c that refer to calling xfree,
where the type in question has changed to std::string.  This patch
removes these obsolete comments.

gdb/ada-varobj.c

@@ -379,16 +379,14 @@ ada_varobj_get_number_of_children (struct value *parent_value,
    whose index is CHILD_INDEX:
 
      - If CHILD_NAME is not NULL, then a copy of the child's name
-       is saved in *CHILD_NAME.  This copy must be deallocated
-       with xfree after use.
+       is saved in *CHILD_NAME.
 
      - If CHILD_VALUE is not NULL, then save the child's value
        in *CHILD_VALUE. Same thing for the child's type with
        CHILD_TYPE if not NULL.
 
      - If CHILD_PATH_EXPR is not NULL, then compute the child's
-       path expression.  The resulting string must be deallocated
-       after use with xfree.
+       path expression.
 
        Computing the child's path expression requires the PARENT_PATH_EXPR
        to be non-NULL.  Otherwise, PARENT_PATH_EXPR may be null if
@@ -805,9 +803,7 @@ ada_varobj_get_type_of_child (struct value *parent_value,
 }
 
 /* Return a string that contains the image of the given VALUE, using
-   the print options OPTS as the options for formatting the result.
-
-   The resulting string must be deallocated after use with xfree.  */
+   the print options OPTS as the options for formatting the result.  */
 
 static std::string
 ada_varobj_get_value_image (struct value *value,
@@ -825,9 +821,7 @@ ada_varobj_get_value_image (struct value *value,
    in the array inside square brackets, but there are situations where
    it's useful to add more info.
 
-   OPTS are the print options used when formatting the result.
-
-   The result should be deallocated after use using xfree.  */
+   OPTS are the print options used when formatting the result.  */
 
 static std::string
 ada_varobj_get_value_of_array_variable (struct value *value,