upgrade to eosio.CDT 1.6.1, remove custom dispatcher

Makefile

@@ -1,2 +1,2 @@
 all:
-	eosio-cpp -Oz -o signup.wasm -I../eosio.contracts-old/eosio.system/include -I../eosio.contracts-old/eosio.system signup.cpp --abigen
+	eosio-cpp -Oz -o signup.wasm -I. -I../eosio.contracts-old/eosio.system/include -I../eosio.contracts-old/eosio.system signup.cpp --abigen

signup.cpp

@@ -1,6 +1,8 @@
 #include "extra.cpp"
 
-void signup::transfer( name from, name to, asset quantity, string memo ) {
+void signup::dummy() { print("DUMMY"); }
+
+void signup::on_transfer( name from, name to, asset quantity, string memo ) {
   // do nothing on outgoing transfers
   if (from == _self || to != _self) {
     return;
@@ -145,14 +147,3 @@ void signup::transfer( name from, name to, asset quantity, string memo ) {
   // Notify a partner about this newly created account
   require_recipient(PARTNER);
 }
-
-//EOSIO_DISPATCH(signup, (transfer))
-// custom dispatcher:
-// https://developers.eos.io/eosio-home/docs/writing-a-custom-dispatcher
-extern "C" {
-  void apply(uint64_t receiver, uint64_t code, uint64_t action) {
-    if(code==name("eosio.token").value && action==name("transfer").value) {
-      execute_action(name(receiver), name(code), &signup::transfer );
-    }
-  }
-};

signup.hpp

@@ -25,10 +25,10 @@ CONTRACT signup : public eosio::contract {
   public:
     using contract::contract;
 
-    ACTION transfer( name   from,
-                     name   to,
-                     asset  quantity,
-                     string memo );
+    ACTION dummy();
+
+    [[eosio::on_notify("eosio.token::transfer")]]
+    void on_transfer( name from, name to, asset quantity, string memo );
 
     signup( name receiver, name code, datastream<const char*> ds ):
       contract( receiver, code, ds ) {}