remove early iteration of concepts (#1123)
remove early iteration of concepts (#1123)

We introduced concepts.csv for CI validation in https://github.com/exercism/v3/pull/856.
It is my understanding that `concepts/` encodes our canonical list.

So concepts.csv is dead code and should be removed from this repository.
petertseng/exercism-rust,exercism/xrust,exercism/xrust,petertseng/exercism-rust,petertseng/exercism-rust