Remove the mojo serial interfaces and related infrastructure.

chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc

Index: chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
diff --git a/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc b/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
index 108ff7e6b1df91d5b428531f373a4b1a43d94e29..78d329947b4c6f2a4ce9d37e86de0c3cd37186d4 100644
--- a/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
+++ b/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
@@ -686,10 +686,6 @@ void ChromeContentBrowserClientExtensionsPart::
 #if defined(ENABLE_WEBRTC)
     command_line->AppendSwitch(::switches::kEnableWebRtcHWH264Encoding);
 #endif
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kEnableMojoSerialService)) {
-      command_line->AppendSwitch(switches::kEnableMojoSerialService);
-    }
   }
 }