Chronos: remove deprecated API from Chronos.

[TheaperDeng]

Remove deprecated API from Chronos

What ?

Deprecated API is now clustered in bigdl.chronos.autots.deprecated. There has been some long dicussion that we need to remove these APIs but no real practise. Recently we are seeing more and more reasons to remove these deprecated APIs.

Why ?

• Deprecated API relies on TF1, which will not be supported by Chronos.

  • TCN, LSTM, S2S, MTNet, AutoEncoder has now been migrated to TF2, some of them can work under TF1, but not all of them.

  • TF1 has conflict with pytorch-lightining on dependencies and conflict with TF2 on python versions.

• Deprecated API now only stays in API doc and 1 use-case notebook with not-recommeded tag. Most of its API usage in our source code is limited to bigdl.chronos.autots.deprecated itself.

• Deprecated API unittest seems to be the most problematic ones in Chronos unittest and keep causing some random freezing(aborting).

How?

We plan to remove deprecated API by 2 steps:

First Step:

• Skip deprecated API unittests Chronos: Skip all deprecated API unittest cases #4400

• Remove deprecated API Doc, and deprecated use-case from document

Second Step:

• Delete deprecated API from src

• Delete deprecated API use-cases