Kernel: Use non-locking {Nonnull,}RefPtr for OpenFileDescription

This patch switches away from {Nonnull,}LockRefPtr to the non-locking
smart pointers throughout the kernel.

I've looked at the handful of places where these were being persisted
and I don't see any race situations.

Note that the process file descriptor table (Process::m_fds) was already
guarded via MutexProtected.

Kernel/Syscalls/anon_create.cpp

@@ -38,7 +38,7 @@ ErrorOr<FlatPtr> Process::sys$anon_create(size_t size, int options)
 
     return m_fds.with_exclusive([&](auto& fds) -> ErrorOr<FlatPtr> {
         auto new_fd = TRY(fds.allocate());
-        fds[new_fd.fd].set(move(description), fd_flags);
+        fds[new_fd.fd].set(description, fd_flags);
         return new_fd.fd;
     });
 }