Cleanup to remove EIA integration tests and other unused files/code

[sachanub]

Issue #, if available:

Description of changes:

The objective of this PR is to cleanup the PyTorch inference toolkit to remove EIA integration tests and other unused files/code. The following need to be removed/modified:

The following need to be removed from the PyTorch inference toolkit:

• Removed the artifacts directory.
• Removed the docker directory.
• Removed buildspec-container-pr.yml. Will delete the corresponding CodeBuild job afterwards.
• Removed old versions from test/container. Specifically, we removed the directories corresponding to versions 1.3.1, 1.5.0, 1.6.0 and 1.10.2.
• Removed any resources and code related to EIA. Specifically, we removed the following:
  • test/container/1.3.1/Dockerfile.eia
  • test/integration/all_models_info.json: Removed any JSON entries corresponding to EIA model artifacts.
  • test/integration/sagemaker/test_default_inference.py: Removed test_default_inference_eia() and any dependencies it requires. Removed any code related to accelerator_type.
  • test/integration/sagemaker/test_mnist.py: Removed test_mnist_eia() and any dependencies it requires. Removed any code related to accelerator_type.
  • test/resources/mnist:
    • Removed the directory default_model_eia.
    • Removed the directory model_eia.
  • test/conftest.py: Removed the code related to accelerator_type.
  • buildspec.yml: Removed any commands related to EIA integration tests.
• Modified .flake8 to include sagemaker_inference in import sequence.
• Modified MANIFEST.in to recursively include src/sagemaker_inference/*.
• Modified README.rst file to no longer reference dependency on base inference toolkit.

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