d8e9a2a Remove "rpc" category from GetWarnings (Wladimir J. van der Laan)
7da3b0a rpc: Move RPC_FORBIDDEN_BY_SAFE_MODE code to reserved section (Wladimir J. van der Laan)
2ae705d Remove Safe mode (Andrew Chow)
Pull request description:
Rebase of #10563. Safe mode was [disabled by default and deprecated in 0.16](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.16.0.md#safe-mode-disabled-by-default), so probably should be removed for 0.17.
> Rationale:
>
> Safe mode is useless. It only disables some RPC commands when large work forks are detected. Nothing else is affected by safe mode. It seems that very few people would be affected by safe mode. The people who use Core as a wallet are primarily using it through the GUI, which safe mode does not effect. In the GUI, transactions will still be made as normal; only a warning is displayed.
>
> I also don't think that we should be disabling RPC commands or any functionality in general. If we do, it should be done consistently, which safe mode is not. If we want to keep the idea of a safe mode around, I think that the current system needs to go first before a new system can be implemented.
Tree-SHA512: 067938f47ca6e879fb6c3c4e21f9946fd7c5da3cde67ef436f1666798c78d049225b9111dc97064f42b3bc549d3915229fa19ad5a634588f381e34fc65d64044
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