Stop linking in desktop/main.cc into the Android build.

shell/android/main.cc

Index: shell/android/main.cc
diff --git a/shell/android/main.cc b/shell/android/main.cc
index aa26a13086d497f86368728544981a546fbd3e0f..c554728b54248420d4faa651b437bdb16cf025a9 100644
--- a/shell/android/main.cc
+++ b/shell/android/main.cc
@@ -214,3 +214,9 @@ bool RegisterShellMain(JNIEnv* env) {
 
 }  // namespace shell
 }  // namespace mojo
+
+// TODO(vtl): Even though main() should never be called, mojo_shell fails to
+// link without it. Figure out if we can avoid this.
+int main(int argc, char** argv) {
+  NOTREACHED();
+}