Use system-provided nlohmann-json library

Removes bundled library and instead pulls in system-provided version. The current Debian oldstable as well as Ubuntu >= focal provide the required packages.

Author: TheAssassin

Diff for: CMakeLists.txt

@@ -13,6 +13,9 @@ if(BUILD_TESTING)
     include(${PROJECT_SOURCE_DIR}/lib/cmake-scripts/include-or-build-gtest.cmake)
 endif()
 
+# dependencies
+find_package(nlohmann_json REQUIRED)
+
 add_subdirectory(lib)
 
 add_subdirectory(src)

Diff for: lib/CMakeLists.txt

@@ -1,9 +1 @@
 add_subdirectory(linuxdeploy EXCLUDE_FROM_ALL)
-
-# required to properly build nlohmann/json v. 2.0.0 on trusty
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
-
-add_library(json INTERFACE)
-set_property(TARGET json PROPERTY INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR}/json/include)
-target_sources(json INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/json/include/json.hpp)