Kernel: Remove sys$select() syscall

Now that the userland has a compatiblity wrapper for select(), the
kernel doesn't need to implement this syscall natively. The poll()
interface been around since 1987, any code still using select()
should be slapped silly.

Note: the SerenityOS source tree mostly uses select() and not poll()
despite SerenityOS having support for poll() since early 2019...

Kernel/CMakeLists.txt

@@ -241,7 +241,6 @@ set(KERNEL_SOURCES
     Syscalls/rename.cpp
     Syscalls/rmdir.cpp
     Syscalls/sched.cpp
-    Syscalls/select.cpp
     Syscalls/sendfd.cpp
     Syscalls/setpgid.cpp
     Syscalls/setuid.cpp