Remove rlib crate-type so that it works with Miri

[danielhenrymantilla]

Having

[lib]
crate-type = ["rlib"]

breaks compilation with miri (cc @RalfJung, maybe that should be mentioned in the README.md).

• repro

  cd $(mktemp -d)
  
  cargo init --lib --name foo
  
  cargo new --lib bar && cargo add --path bar{,}  # cargo-edit
  
  cat >>bar/Cargo.toml<<\#\ END
  [lib]
  crate-type = ["rlib"]
  # END
  
  echo 'use ::bar;' >> src/lib.rs
  
  cargo miri test

Now, I cannot remember why I put that "rlib" thing to begin with, but after looking in more detail into what it does, I think it's doing do more harm than any potential good (or, at least, I should be using ["rlib", "lib"] to avoid removing "lib" when with some compiler (such as miri's?) it isn't an alias for "rlib". And until somebody observes some breakage from replacing "rlib" back with the default "lib", I will be favoring the default setting).

[RalfJung]

maybe that should be mentioned in the README.md

At first sight this sounds like a bug, though depending on how cargo handles this the bug might be hard to fix. Could you open an issue in the Miri issue tracker, together with your reproducible example?

[danielhenrymantilla]

Since rust-lang/miri#1709 has been merged, which solves rust-lang/miri#1691, the issue tracking the limitation that motivated this very PR, the PR is no longer needed and can be dismissed.