Reland "net: Remove linux specific files from Lacros."

This is a reland of commit 3e18980f0b

It's reverted due to net_watcher failure.
Removed network_change_notifier_linux path from net_watcher.
The additional part for fixing revert can be seen by comparing with
patchset 1.

Original change's description:
> net: Remove linux specific files from Lacros.
>
> This CL removes network_change_notifier_linux files since they are no
> longer needed.
> It also removew proxy_config_service_linux files which were also
> deprecated as Lacros uses proxy_config_service_lacros instead.
> (crrev.com/c/3122991).
>
> Bug: 1331211
> Change-Id: I602f1db984e09092169dc467b919fbee69da15c0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4025444
> Auto-Submit: Eriko Kurimoto <elkurin@chromium.org>
> Reviewed-by: Adam Rice <ricea@chromium.org>
> Commit-Queue: Adam Rice <ricea@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1070942}

Bug: 1331211
Change-Id: I019a11f47e002524d18cb40501ce1dc5e0638d3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4025565
Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Eriko Kurimoto <elkurin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1071430}

net/BUILD.gn

@@ -1184,10 +1184,8 @@ component("net") {
     ]
   }
 
-  if (is_linux || is_chromeos_lacros) {
+  if (is_linux) {
     sources += [
-      # TODO(crbug.com/1331211): Remove network_change_notifier_linux for Lacros
-      # when BindNertworkChangeManager is supported by default.
       "base/network_change_notifier_linux.cc",
       "base/network_change_notifier_linux.h",
       "proxy_resolution/proxy_config_service_linux.cc",
@@ -4642,14 +4640,15 @@ test("net_unittests") {
     ]
   }
 
+  if (is_linux) {
+    sources += [ "proxy_resolution/proxy_config_service_linux_unittest.cc" ]
+  }
+
   if (is_linux || is_chromeos) {
     sources += [
       "base/address_tracker_linux_unittest.cc",
       "base/network_interfaces_linux_unittest.cc",
     ]
-    if (!is_chromeos_ash) {
-      sources += [ "proxy_resolution/proxy_config_service_linux_unittest.cc" ]
-    }
   }
 
   if (is_mac) {

net/tools/net_watcher/net_watcher.cc

@@ -32,9 +32,7 @@
 #include "net/proxy_resolution/proxy_config_service.h"
 #include "net/proxy_resolution/proxy_config_with_annotation.h"
 
-// TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
+#if BUILDFLAG(IS_LINUX)
-// of lacros-chrome is complete.
-#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS_LACROS)
 #include "net/base/network_change_notifier_linux.h"
 #endif
 
@@ -46,7 +44,7 @@ namespace {
 
 // TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
 // of lacros-chrome is complete.
-#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS_LACROS)
+#if BUILDFLAG(IS_LINUX)
 // Flag to specifies which network interfaces to ignore. Interfaces should
 // follow as a comma seperated list.
 const char kIgnoreNetifFlag[] = "ignore-netif";
@@ -165,9 +163,7 @@ int main(int argc, char* argv[]) {
 
   NetWatcher net_watcher;
 
-// TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
+#if BUILDFLAG(IS_LINUX)
-// of lacros-chrome is complete.
-#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS_LACROS)
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   std::string ignored_netifs_str =
       command_line->GetSwitchValueASCII(kIgnoreNetifFlag);