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 LAG1

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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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     TAU : TIME ;     (* Filter time constant *)

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     CYCLE : TIME ;   (* Sampling time interval *)

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   END_VAR

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

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   VAR K : REAL ;     (* Smoothing constant, 0.0<=K<1.0 *)

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   END_VAR

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   IF RUN THEN XOUT := XOUT + K * (XIN - XOUT) ;

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   ELSE XOUT := XIN ;

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        K := TIME_TO_REAL(CYCLE) / TIME_TO_REAL(CYCLE + TAU) ;

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   END_IF ;

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 END_FUNCTION_BLOCK

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