move type resolution to compiler

from risc_value.
also unite mock compilers

test/mom/instruction/helper.rb

@@ -1,21 +1,6 @@
 require_relative '../helper'
 
 module Mom
-  class CompilerMock
-    # resolve a symbol to a type. Allowed symbols are :frame , :receiver and arguments
-    # which return the respective types, otherwise nil
-    def resolve_type( name )
-        return nil
-    end
-    def use_reg( type )
-      Risc.tmp_reg(type )
-    end
-    def reset_regs
-
-    end
-    def add_constant(c)
-    end
-  end
   class InstructionMock < Instruction
   end
 end