Headless: Remove obsolete Mojo code and some other obsolete APIs

headless/lib/headless_browsertest_resources.grd

Index: headless/lib/headless_browsertest_resources.grd
diff --git a/headless/lib/headless_browsertest_resources.grd b/headless/lib/headless_browsertest_resources.grd
deleted file mode 100644
index db803c1609df97570cd59b769b81788d6afc02a1..0000000000000000000000000000000000000000
--- a/headless/lib/headless_browsertest_resources.grd
+++ /dev/null
@@ -1,16 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-
-<grit latest_public_release="0" current_release="1">
-  <outputs>
-    <output filename="grit/headless_browsertest_resources.h" type="rc_header">
-      <emit emit_type='prepend'></emit>
-    </output>
-    <output filename="headless_browsertest_resources.pak" type="data_package" />
-  </outputs>
-  <translations />
-  <release seq="1">
-    <includes>
-      <include name="IDR_HEADLESS_EMBEDDER_TEST_MOJOM_JS" file="${mojom_root}\headless\lib\embedder_test.mojom.js" use_base_dir="false" type="BINDATA" />
-    </includes>
-  </release>
-</grit>