[cob_light] removed unused Boost signals dependency

[lopsided98]

cob_light depends on Boost signals2, which is a header only library that does not need to be found using find_package. The CMakeLists.txt tries to find Boost signals (v1). This library was removed in Boost 1.69, causing this package to fail to build.

[fmessmer]

sounds reasonable

just for my understanding:
in what architecture/distro/setup do you get build errors?
can you post a log?

[lopsided98]

I am using Nix, but this problem will occur on any distribution with Boost >=1.69. This is the error message:

CMake Error at /nix/store/0rwxndjblrj8ashnfv0g9sxcnv2mdiw3-cmake-3.15.4/share/cmake-3.15/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
  Could NOT find Boost (missing: signals) (found version "1.69.0")
Call Stack (most recent call first):
  /nix/store/0rwxndjblrj8ashnfv0g9sxcnv2mdiw3-cmake-3.15.4/share/cmake-3.15/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
  /nix/store/0rwxndjblrj8ashnfv0g9sxcnv2mdiw3-cmake-3.15.4/share/cmake-3.15/Modules/FindBoost.cmake:2161 (find_package_handle_standard_args)
  CMakeLists.txt:8 (find_package)


-- Configuring incomplete, errors occurred!

Many ROS packages have this same problem: ros-planning/navigation#945, ros/geometry2#354, ros/geometry#180, moveit/moveit#1353, ros/ros_comm#1580, PR2/pr2_common_actions#39, ros-perception/calibration#43

[fmessmer]

thx for the patch and the explanation....I took care of other cob_* repos with the same problem....