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.

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FUNCTION WEIGH : WORD     (* BCD encoded *)

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  VAR_INPUT  (* "EN" input is used to indicate "scale ready" *)

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    weigh_command : BOOL;

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    gross_weight : WORD ; (* BCD encoded *)

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    tare_weight : INT ;

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  END_VAR

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(* Function Body *)

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IF weigh_command THEN

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  WEIGH := INT_TO_BCD (BCD_TO_INT(gross_weight) - tare_weight);

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END_IF ;

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END_FUNCTION                     (* Implicit "ENO" *)