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 <rust-lang/rust#57571>

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

build.rs

@@ -85,34 +85,29 @@ fn build(frameworks_path: &str) {
     use std::env;
     use std::path::PathBuf;
 
-    let mut frameworks = vec![];
     let mut headers = vec![];
 
     #[cfg(feature = "audio_toolbox")]
     {
         println!("cargo:rustc-link-lib=framework=AudioToolbox");
-        frameworks.push("AudioToolbox");
         headers.push("AudioToolbox.framework/Headers/AudioToolbox.h");
     }
 
     #[cfg(feature = "audio_unit")]
     {
         println!("cargo:rustc-link-lib=framework=AudioUnit");
-        frameworks.push("AudioUnit");
         headers.push("AudioUnit.framework/Headers/AudioUnit.h");
     }
 
     #[cfg(feature = "core_audio")]
     {
         println!("cargo:rustc-link-lib=framework=CoreAudio");
-        frameworks.push("CoreAudio");
         headers.push("CoreAudio.framework/Headers/CoreAudio.h");
     }
 
     #[cfg(feature = "open_al")]
     {
         println!("cargo:rustc-link-lib=framework=OpenAL");
-        frameworks.push("OpenAL");
         headers.push("OpenAL.framework/Headers/al.h");
         headers.push("OpenAL.framework/Headers/alc.h");
     }
@@ -121,7 +116,6 @@ fn build(frameworks_path: &str) {
     {
         if std::env::var("TARGET").unwrap().contains("apple-darwin") {
             println!("cargo:rustc-link-lib=framework=CoreMIDI");
-            frameworks.push("CoreMIDI");
             headers.push("CoreMIDI.framework/Headers/CoreMIDI.h");
         }
     }
@@ -140,12 +134,6 @@ fn build(frameworks_path: &str) {
         builder = builder.header(absolute_path);
     }
 
-    // Link to all frameworks.
-    for relative_path in frameworks {
-        let link_instruction = format!("#[link = \"{}/{}\"]", frameworks_path, relative_path);
-        builder = builder.raw_line(link_instruction);
-    }
-
     // Generate the bindings.
     builder = builder
         .trust_clang_mangling(false)