[formrecognizer] Remove get children methods (#21602)

* remove get_words and get_lines methods on models

* remove references to parent elements

* remove extra tests

* delete recordings

* update sample to use document get_words

* remove references to deleted methods in samples

* update changelog

* remove references to old samples in README

* add error for DocumentLines converted from dicts

* shorten long line

Author: catalinaperalta

sdk/formrecognizer/azure-ai-formrecognizer/CHANGELOG.md

@@ -3,9 +3,8 @@
 ## 3.2.0b2 (2021-11-09)
 
 ### Features Added
-- Added `get_words` methods on `AnalyzedDocument`, `DocumentEntity`, `DocumentField`, `DocumentLine`, `DocumentKeyValueElement`, `DocumentTable`, `DocumentTableCell`.
-- Added `get_lines` methods on `AnalyzedDocument`, `DocumentEntity`, `DocumentField`, `DocumentKeyValueElement`, `DocumentTable`, `DocumentTableCell`.
-- Added samples showing how to use `get_words` and `get_lines` under `/samples/v3.2-beta`: `sample_get_document_elements.py` and `sample_get_document_elements_async.py`.
+- Added `get_words()` on `DocumentLine`.
+- Added samples showing how to use `get_words()` on a `DocumentLine` under `/samples/v3.2-beta`: `sample_get_words_on_document_line.py` and `sample_get_words_on_document_line_async.py`.
 
 ### Breaking Changes
 - Renamed `DocumentElement` to `DocumentContentElement`.