Remove dependency on openssl

[Centril]

It's being pulled in by reqwest, which comes as a default feature we're not using (see https://github.com/seanmonstar/reqwest/blob/master/Cargo.toml)

We're also using it in standalone to generate keys, which can be delegated to shell calls.

Removing this dependency removes a long chunk of compilation time on windows.

[jdetter]

Removing this dependency removes a long chunk of compilation time on windows.

Really it's hard to understate the amount of time this is taking in windows. I believe the vast majority of the time spent compiling SpacetimeDB on windows is just openssl.

[mamcx]

For generating the keys we can use ring