revert commits improved performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR)

Following commits are reverted:
mjsousa 0b275a2 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- increase hardcoded limit to 499
mjsousa 2228799 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- Add comments!!
mjsousa ce81fa6 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR)"

The reason is that they cause regression in some cases (if function is
used as argument for function block, for example) and this is not
fixed for a long time.

FUNCTION WEIGH : WORD     (* BCD encoded *)
  VAR_INPUT  (* "EN" input is used to indicate "scale ready" *)
    weigh_command : BOOL;
    gross_weight : WORD ; (* BCD encoded *)
    tare_weight : INT ;
  END_VAR
(* Function Body *)
	LD	weigh_command	
	JMPC	WEIGH_NOW	
	ST	ENO	(* No weighing, 0 to "ENO" *)
	RET		
WEIGH_NOW:	LD	gross_weight	
	BCD_TO_INT		
	SUB	tare_weight	
	INT_TO_BCD		(* Return evaluated weight *)
	ST	WEIGH	

END_FUNCTION                     (* Implicit "ENO" *)