* move fluid.utils to paddle.utils.layers_utils

* fix error

* delete original fluid layers utils

* remove import and old utils

* remove more old utils import

* change import path of fill_constant in the layers_utils.py

* fix mistake

* fix error

* expose in __init__.py

* for comment

* when change the ref of func is_sequence, it should change to the root of is_sequence instead

* for codecheck