Problem: basic json-rpc failed on pruned nodes

[yihuang]

Solution:

• Make basic json-rpc apis (get tx, get block) works on pruned nodes
• Test with integration tests

ref: #451, improve user experience of pruned nodes.

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PR Checklist:

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• Does your PR follow the C4 patch requirements?
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• Have you included tests for any non-trivial functionality?
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Thank you for your code, it's appreciated! :)

[adu-crypto]

lgtm