remove MethodEnter Instructions

only resolved to SaveReturn anyway
also Halt instruction wasn’t used, gone
passes changed to start at register

lib/virtual/passes/enter_implementation.rb

@@ -1,15 +0,0 @@
-module Virtual
-
-  class EnterImplementation
-    def run block
-      block.codes.dup.each do |code|
-        next unless code.is_a? Virtual::MethodEnter
-        new_codes = []
-        # save return register to the message at instance return_address
-        new_codes << Register.save_return(code, :message , :return_address)
-        block.replace(code , new_codes )
-      end
-    end
-  end
-  Virtual.machine.add_pass "Virtual::EnterImplementation"
-end