cmake: do not explicitly require boost_system

It is a header-only library that is no longer available as a stub
library in `boost-1.89`.

Related: #234

Author: kdudka

src/CMakeLists.txt

@@ -45,7 +45,6 @@ find_package(Boost REQUIRED
     COMPONENTS filesystem
                program_options
                regex
-               system
     OPTIONAL_COMPONENTS json
                         nowide)
 include_directories(SYSTEM ${Boost_INCLUDE_DIRS})