Remove support for hardware registers in TAC

Rakefile

@@ -43,19 +43,10 @@ end
 
 desc 'Convert previous stage language into the current stage language'
 task :convert do
-  File.open('boot/stage17/cl.elna', 'w') do |current_stage|
-    File.readlines('boot/stage16/cl.elna').each do |line|
+  File.open('boot/stage18/cl.elna', 'w') do |current_stage|
+    File.readlines('boot/stage17/cl.elna').each do |line|
         current_stage << line
     end
-    current_stage << <<~STAGE
-
-      proc f(x: ElnaTreeExpression);
-      var
-      	y: Word;
-      begin
-      	y := x.kind
-      end;
-    STAGE
   end
 end