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_BLOCK AVERAGE

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   VAR_INPUT

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     RUN : BOOL ;      (* 1 = run, 0 = reset *)

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     XIN : REAL ;     (* Input variable *)

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     N   : INT ;      (* 0 <= N < 128 or manufacturer- *)

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   END_VAR            (*      specified maximum value  *)

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   VAR_OUTPUT XOUT : REAL ; END_VAR (* Averaged output *)

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   VAR SUM  : REAL := 0.0; (* Running sum *)

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       FIFO : DELAY ;      (* N-Element FIFO *)

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   END_VAR

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   SUM := SUM - FIFO.XOUT ;

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   FIFO (RUN := RUN , XIN := XIN, N := N) ;

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   SUM := SUM + FIFO.XOUT ;

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   IF RUN THEN XOUT := SUM/N ;

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   ELSE SUM := N*XIN ; XOUT := XIN ;

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   END_IF ;

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 END_FUNCTION_BLOCK

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