Update for latest changes to oe-core

[rossburton]

oe-core now has Rust integrated, so there's eg cargo.bbclass in oe-core.

This layer should merge any improvements it has into oe-core, and remove the classes. Ideally, it would simply be a few recipes which provide the same contents as the source-based packages in oe-core, but from the binaries, so it's a drop-in replacement to improve build times.