Always use builtin JThread library

cmake/Modules/FindJthread.cmake

src/CMakeLists.txt

src/ban.cpp

src/ban.h

src/client.cpp

src/client.h

src/debug.cpp

src/jthread/CMakeLists.txt

src/jthread/jthread.h

src/jthread/pthread/jmutex.cpp

src/jthread/pthread/jthread.cpp

src/jthread/win32/jmutex.cpp

src/jthread/win32/jthread.cpp

src/profiler.h

src/quicktune.cpp

src/script/cpp_api/s_base.h

src/server.cpp

src/settings.h

src/threads.h

src/util/container.h