Move ValidateAdbModeFlag to flags.cc

This is a step towards breaking the dependency from flags.cc on launch.h

Bug: 135293952
Test: Build and run
Change-Id: Ib62953d309cbc868bd45954860e059372061ad0e
diff --git a/host/commands/launch/flags.cc b/host/commands/launch/flags.cc
index 22eec39..3dff3bc 100644
--- a/host/commands/launch/flags.cc
+++ b/host/commands/launch/flags.cc
@@ -624,6 +624,15 @@
   auto decomp_proc = decomp_cmd.Start(false);
   return decomp_proc.Started() && decomp_proc.Wait() == 0;
 }
+
+void ValidateAdbModeFlag(const vsoc::CuttlefishConfig& config) {
+  auto adb_modes = config.adb_mode();
+  adb_modes.erase(vsoc::AdbMode::Unknown);
+  if (adb_modes.size() < 1) {
+    LOG(INFO) << "ADB not enabled";
+  }
+}
+
 } // namespace
 
 namespace {