[dart:io] Remove DART_IO_DISABLED

runtime/bin/io_impl_sources.gni

Index: runtime/bin/io_impl_sources.gni
diff --git a/runtime/bin/io_impl_sources.gni b/runtime/bin/io_impl_sources.gni
index e4396dcaeaa9486f2f7e2025a7e397ac4fd5779e..4c6b6cefb314f683b7e876dc6d6ec43d01416234 100644
--- a/runtime/bin/io_impl_sources.gni
+++ b/runtime/bin/io_impl_sources.gni
@@ -15,7 +15,6 @@ io_impl_sources = [
   "eventhandler_linux.h",
   "eventhandler_macos.cc",
   "eventhandler_macos.h",
-  "eventhandler_unsupported.cc",
   "eventhandler_win.cc",
   "eventhandler_win.h",
   "file_system_watcher.cc",
@@ -24,23 +23,19 @@ io_impl_sources = [
   "file_system_watcher_fuchsia.cc",
   "file_system_watcher_linux.cc",
   "file_system_watcher_macos.cc",
-  "file_system_watcher_unsupported.cc",
   "file_system_watcher_win.cc",
   "filter.cc",
   "filter.h",
-  "filter_unsupported.cc",
   "io_service.cc",
   "io_service.h",
   "io_service_no_ssl.cc",
   "io_service_no_ssl.h",
-  "io_service_unsupported.cc",
   "platform.cc",
   "platform.h",
   "platform_android.cc",
   "platform_fuchsia.cc",
   "platform_linux.cc",
   "platform_macos.cc",
-  "platform_unsupported.cc",
   "platform_win.cc",
   "process.cc",
   "process.h",
@@ -48,7 +43,6 @@ io_impl_sources = [
   "process_fuchsia.cc",
   "process_linux.cc",
   "process_macos.cc",
-  "process_unsupported.cc",
   "process_win.cc",
   "reference_counting.h",
   "root_certificates_unsupported.cc",
@@ -77,13 +71,11 @@ io_impl_sources = [
   "socket_base_linux.h",
   "socket_base_macos.cc",
   "socket_base_macos.h",
-  "socket_base_unsupported.cc",
   "socket_base_win.cc",
   "socket_base_win.h",
   "socket_fuchsia.cc",
   "socket_linux.cc",
   "socket_macos.cc",
-  "socket_unsupported.cc",
   "socket_win.cc",
   "stdio.cc",
   "stdio.h",
@@ -91,7 +83,6 @@ io_impl_sources = [
   "stdio_fuchsia.cc",
   "stdio_linux.cc",
   "stdio_macos.cc",
-  "stdio_unsupported.cc",
   "stdio_win.cc",
   "sync_socket.cc",
   "sync_socket.h",
@@ -99,6 +90,5 @@ io_impl_sources = [
   "sync_socket_fuchsia.cc",
   "sync_socket_linux.cc",
   "sync_socket_macos.cc",
-  "sync_socket_unsupported.cc",
   "sync_socket_win.cc",
 ]