Use simple-mermaid from crates-io (#3304)

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.

---------

Signed-off-by: Oliver Tale-Yazdi <[email protected]>