Removing superfluous 'execute_process' command which always runs even when the cfg file doesn't change.

Currently, dynamic_reconfigure will _always_ re-generate files when cmake configure is run. This Causes a LOT of unnecessary re-compilation. Furthermore, it looks like the configure files are being generated twice when they need to be. This patch removes the 'execute_process' cmake command which runs the same exact command as the 'add_custom_command' cmake command that appears a few lines below.