return the linker from mom_compiler

linker holds assemblers
assemblers come from method compilation
and so the layers come into focus

test/mom/test_method_compiler.rb

@@ -1,44 +0,0 @@
-require_relative "helper"
-
-module Mom
-  class TestMomCompiler < MiniTest::Test
-    include MomCompile
-
-    def setup
-      Parfait.boot!
-      @comp = compile_mom( "class Test ; def main(); return 1; end; end;")
-    end
-
-    def test_class
-      assert_equal MomCompiler , @comp.class
-    end
-    def test_compilers
-      assert_equal 1 , @comp.method_compilers.length
-    end
-    def test_has_translate
-      assert @comp.translate(:interpreter)
-    end
-  end
-  class TestMomCompilerTranslate < MiniTest::Test
-    include MomCompile
-
-    def setup
-      Parfait.boot!
-      @comp = compile_mom( "class Test ; def main(); return 1; end; end;")
-      @trans = @comp.translate(:interpreter)
-    end
-
-    def test_translate_class
-      assert_equal Array , @trans.class
-    end
-    def test_translate_assemblers
-      assert_equal Risc::Assembler , @trans.first.class
-    end
-    def test_assembler_code
-      assert_equal Risc::Label , @trans.first.instructions.class
-    end
-    def test_assembler_assembled
-      assert_equal Risc::LoadConstant , @trans.first.instructions.next.class
-    end
-  end
-end