Remove #[link] attributes
Remove #[link] attributes

They cause the following warnings:
warning: attribute must be of the form `#[link(name = "...", /*opt*/ kind = "dylib|static|...",
                                               /*opt*/ cfg = "...")]`
 --> /tmp/coreaudio-sys/target/x86_64-apple-darwin/debug/build/coreaudio-sys-0d8fd082e359c2ec/out/coreaudio.rs:3:1
  |
3 | #[link = "/tmp/MacOSX10.14.sdk/System/Library/Frameworks/AudioToolbox"]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(ill_formed_attribute_input)] on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>

And they are actually redundant with the cargo:rustc-link-lib lines the
build script prints already.

RustAudio/coreaudio-sys