[vm/ffi] Remove deprecated FfiNative

TEST=pkg/analyzer/test/
TEST=CI build with class removed from `dart:ffi`

Closes: https://github.com/dart-lang/sdk/issues/53923
CoreLibraryReviewExempt: VM & dart2wasm only.
Change-Id: I45a39b623754f9f1b65cac55ea9adae390199f5d
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm64c-try,analyzer-analysis-server-linux-try,analyzer-mac-release-try,dart-sdk-linux-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/336960
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>

pkg/mmap/lib/src/mmap_impl.dart

@@ -2,9 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// File is compiled with checked in SDK, update [FfiNative]s to [Native] when
-// SDK is rolled.
-
 // ignore_for_file: camel_case_types
 // ignore_for_file: deprecated_member_use
 // ignore_for_file: non_constant_identifier_names
@@ -25,14 +22,12 @@ external int close(int fd);
 // void* mmap(void* addr, size_t length,
 //            int prot, int flags,
 //            int fd, off_t offset)
-@FfiNative<
-    Pointer<Uint8> Function(
-        Pointer<Uint8>, Size, Int, Int, Int, IntPtr)>("mmap")
+@Native<Pointer<Uint8> Function(Pointer<Uint8>, Size, Int, Int, Int, IntPtr)>()
 external Pointer<Uint8> mmap(
     Pointer<Uint8> address, int len, int prot, int flags, int fd, int offset);
 
 // int munmap(void *addr, size_t length)
-@Native<IntPtr Function(Pointer<Uint8> address, Size len)>(symbol: "munmap")
+@Native<IntPtr Function(Pointer<Uint8> address, Size len)>()
 external int munmap(Pointer<Uint8> address, int len);
 
 final DynamicLibrary processSymbols = DynamicLibrary.process();