Remove unused abi attributes.

They've been replaced by putting the name on the extern block.

  #[abi = "foo"]

goes to

  extern "foo" { }

Closes #9483.

doc/tutorial-ffi.md

@@ -415,21 +415,18 @@ fn main() {
 
 Most foreign code exposes a C ABI, and Rust uses the platform's C calling convention by default when
 calling foreign functions. Some foreign functions, most notably the Windows API, use other calling
-conventions. Rust provides the `abi` attribute as a way to hint to the compiler which calling
-convention to use:
+conventions. Rust provides a way to tell the compiler which convention to use:
 
 ~~~~
 #[cfg(target_os = "win32")]
-#[abi = "stdcall"]
 #[link_name = "kernel32"]
-extern {
+extern "stdcall" {
     fn SetEnvironmentVariableA(n: *u8, v: *u8) -> int;
 }
 ~~~~
 
-The `abi` attribute applies to a foreign module (it cannot be applied to a single function within a
-module), and must be either `"cdecl"` or `"stdcall"`. The compiler may eventually support other
-calling conventions.
+This applies to the entire `extern` block, and must be either `"cdecl"` or
+`"stdcall"`. The compiler may eventually support other calling conventions.
 
 # Interoperability with foreign code
 

src/libextra/time.rs

@@ -19,8 +19,7 @@ static NSEC_PER_SEC: i32 = 1_000_000_000_i32;
 pub mod rustrt {
     use super::Tm;
 
-    #[abi = "cdecl"]
-    extern {
+    extern "cdecl" {
         pub fn get_time(sec: &mut i64, nsec: &mut i32);
         pub fn precise_time_ns(ns: &mut u64);
         pub fn rust_tzset();

src/libextra/unicode.rs

@@ -162,8 +162,7 @@ pub mod icu {
 
         // #[link_name = "icuuc"]
         #[link_args = "-licuuc"]
-        #[abi = "cdecl"]
-        extern {
+        extern "cdecl" {
             pub fn u_hasBinaryProperty(c: UChar32, which: UProperty) -> UBool;
             pub fn u_isdigit(c: UChar32) -> UBool;
             pub fn u_islower(c: UChar32) -> UBool;

src/librustc/lib/llvm.rs

@@ -300,8 +300,7 @@ pub mod llvm {
 
     #[link_args = "-Lrustllvm -lrustllvm"]
     #[link_name = "rustllvm"]
-    #[abi = "cdecl"]
-    extern {
+    extern "cdecl" {
         /* Create and destroy contexts. */
         pub fn LLVMContextCreate() -> ContextRef;
         pub fn LLVMContextDispose(C: ContextRef);

src/libstd/io.rs

@@ -76,9 +76,8 @@ pub type fd_t = c_int;
 pub mod rustrt {
     use libc;
 
-    #[abi = "cdecl"]
     #[link_name = "rustrt"]
-    extern {
+    extern "cdecl" {
         pub fn rust_get_stdin() -> *libc::FILE;
         pub fn rust_get_stdout() -> *libc::FILE;
         pub fn rust_get_stderr() -> *libc::FILE;