Icon or eyesore? The perception of Carlsbad’s 400-foot-tall coastal smokestack is in the eye of the beholder. The old chimney, a concrete exclamation point in the sky, soon could be gone. Demolition of the Encina power plant is scheduled to begin by the end of this year, after a new, more efficient plant built at the rear of the Carlsbad Boulevard property, north of Cannon Road, replaced it last December.