build: remove enable_run_as_node build flag (#38413)

* feat: remove enable_run_as_node flag

* drop features.isRunAsNodeEnabled()

* use IsEnvSet() helper in electron_main_linux.cc

* cleanup [[maybe_unused]]

---------

Co-authored-by: Milan Burda <miburda@microsoft.com>

buildflags/BUILD.gn

@@ -9,7 +9,6 @@ buildflag_header("buildflags") {
   header = "buildflags.h"
 
   flags = [
-    "ENABLE_RUN_AS_NODE=$enable_run_as_node",
     "ENABLE_OSR=$enable_osr",
     "ENABLE_VIEWS_API=$enable_views_api",
     "ENABLE_PDF_VIEWER=$enable_pdf_viewer",

buildflags/buildflags.gni

@@ -3,9 +3,6 @@
 # found in the LICENSE file.
 
 declare_args() {
-  # Allow running Electron as a node binary.
-  enable_run_as_node = true
-
   enable_osr = true
 
   enable_views_api = true