With no rain or even clouds to warn him of the danger, death came literally out of the blue Thursday to a self-employed landscaper. The killer was a powerful bolt of lightning that cracked through perfectly clear skies. David Canales, 41, of West Miami-Dade, was on the job at a Pinecrest home when the bolt hit. It first seared a tree, then traveled and struck Canales, standing nearby. Experts said Canales was killed by a weather phenomenon fittingly called a ''bolt from the blue'' or ''dry lightning'' because it falls from clear, blue skies.