Remove nimble from nim compilation
As of https://github.com/nim-lang/nimble/pull/1131, `nimble` can build nim - however, as part of building nim-the-compiler, it also builds a toolchain including `nimble` - this can lead to the user instance of nimble being replaced with the version that gets compiled with nim.

when `nimble` installs `nim` as part of the dependencies of a project, it should not compile `nimble` and other tooling as this makes `nimble shell` and similar behave inconsistently as `nimble` gets replaced by a different version.
