Co-authored-by: TianYuan <white-sky@qq.com>

Co-authored-by: N0x45f <wangzhen45@baidu.com>

* fix dygraph to static for tacotron2, test=doc

* Fix dy2st error for taco2

* Update attentions.py

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Co-authored-by: N0x45f <wangzhen45@baidu.com>

* remove fluid api and useless import.

* fix variable name

* add simple adeadelta optimizer.

* remove useless log

* remove useless and fluid import.

* add framework.dygraph_only back