Re https://github.com/paritytech/polkadot-sdk/issues/2922

Changes:
- Use crates-io version of simple-mermaid as
[v0.1.1](https://github.com/glueball/simple-mermaid/releases/tag/v0.1.1)
supports no-std.
- Remove from `frame` since i did not see it used.

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Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>