In the midst of all the other activities last week, Mojave became the home of yet another retired airliner, this time ex-Delta 757 N606DL. What made things interesting, however, is ''how'' it got here. The plane was originally retired to Victorville airport, where it was due to be scrapped, but the fuselage "tube" was purchased for use as a training device, to be staged at Mojave. Aircraft Recycling Corp., which runs the Victorville scrapyard, cut the wings, tail and cockpit off, and then Aviation Warehouse manufactured a set of special wheels. Because of the height of this oversized load, the overpasses along U.S. Highway 58 couldn't be negotiated, and the plane had to be trucked north to Inyokern and then down to Mojave, sending it through Red Rock Canyon, where numerous TV shows and car commercials have been filmed.