cleanup cargo config file as all unstable features are now managed th…

[yogh333]

…rough a global /config.toml file in the Docker full image

[yhql]

Not sure we should move those particular flags, because the app would not build without the ledger-app-builder.
Some config flags like config-host, that may be necessary for the 'lite' docker image which uses musl can be put in a global config file because they're tied to the host and not the app.

[yogh333]

@yhql Ok so your suggestion is to keep this section:

[unstable]
build-std = ["core"]
build-std-features = ["compiler-builtins-mem"]

in the app's .cargo/config.toml (and removing it from the global $CARGO_HOME/config.toml) ?

[yogh333]

I have updated the global config file accordingly: LedgerHQ/ledger-app-builder@4e28c73

[yhql]

Yes. I think if we merge #30 we'll see that this PR fails the currently non-docker build

[yogh333]

Ok I close this PR.