There are two programs that can take care of that pretty easily: Photoshop and GIMP. Both have content-generation tools that can fill in the area of the cable with content generated from its surroundings. In Photoshop, it is called Content-Aware Fill, and in GIMP it is called Resynthesizer. The latter is getting a bit dated, and it may not be entirely effective, however it should still do the job.
In Photoshop, Content-Aware Fill should be able to eliminate the cable in a few seconds flat...it is really as simple as selecting the cable with the selection tool, hitting the delete key, and choosing Content-Aware Fill as the fill mode. Photoshop should do all the hard work for you by generating blue sky and tree content.
In the absence of Photoshop CS5, some clever use of cloning and/or healing tools should also do the job, although it will require some more careful application and considerably more time. You can probably use the spot healing tool in Lightroom for the same purpose, however it is more limited than what you have with Photoshop or GIMP.