Boost 1.89 Build Fix

[yate]

Currently fails to build with boost 1.89 with

CMake Error at /usr/lib/cmake/Boost-1.89.0/BoostConfig.cmake:141 (find_package):
  Could not find a package configuration file provided by "boost_system"
  (requested version 1.89.0) with any of the following names:

    boost_systemConfig.cmake
    boost_system-config.cmake

  Add the installation prefix of "boost_system" to CMAKE_PREFIX_PATH or set
  "boost_system_DIR" to a directory containing one of the above files.  If
  "boost_system" provides a separate development package or SDK, be sure it
  has been installed.
Call Stack (most recent call first):
  /usr/lib/cmake/Boost-1.89.0/BoostConfig.cmake:262 (boost_find_component)
  /usr/share/cmake/Modules/FindBoost.cmake:609 (find_package)
  libgrive/CMakeLists.txt:8 (find_package)

In 1.69, Boost transitioned the system library to header only so it's no longer required to link it. 1.89 seems to have removed the stub library entirely.

I didn't see any uses of the system library anywhere in the code, but if it's actually needed the required Boost version should probably be increased to 1.69