Created by: reyoung

We should remove DeviceContext::Finish because

1. If CUDA or another device has errors when invoking Wait method, the error should be thrown by Wait.
2. These two APIs are confusing. How do developers pick whether should be invoked?
3. The meaning of Finish is not clear. Finialize always means delete or destroy, not complete.

https://github.com/PaddlePaddle/Paddle/blob/584c9cfc82bedf7fd1e293b9e295d2fd5a196409/paddle/platform/device_context.cc#L127-L130