Remove the mojo serial interfaces and related infrastructure.

extensions/renderer/BUILD.gn

Index: extensions/renderer/BUILD.gn
diff --git a/extensions/renderer/BUILD.gn b/extensions/renderer/BUILD.gn
index cf16edbdeecc006e0ee6b1b2063c3bd8c2b0b5cf..bfdc6977711d27c47c73111c1658e4b12b7e66fa 100644
--- a/extensions/renderer/BUILD.gn
+++ b/extensions/renderer/BUILD.gn
@@ -251,9 +251,6 @@ source_set("unit_tests") {
   sources = [
     "activity_log_converter_strategy_unittest.cc",
     "api/mojo_private/mojo_private_unittest.cc",
-    "api/serial/data_receiver_unittest.cc",
-    "api/serial/data_sender_unittest.cc",
-    "api/serial/serial_api_unittest.cc",
     "api_test_base.cc",
     "api_test_base.h",
     "api_test_base_unittest.cc",
@@ -265,7 +262,6 @@ source_set("unit_tests") {
     "module_system_test.h",
     "module_system_unittest.cc",
     "mojo/keep_alive_client_unittest.cc",
-    "mojo/stash_client_unittest.cc",
     "safe_builtins_unittest.cc",
     "scoped_web_frame.cc",
     "scoped_web_frame.h",
@@ -277,7 +273,6 @@ source_set("unit_tests") {
   deps = [
     ":renderer",
     "//base",
-    "//device/serial:test_support",
     "//extensions:extensions_renderer_resources",
 
     # TODO(brettw) these tests should not be including headers from browser.