queue: Drop superfluous #include qemu/atomic.h

queue: Drop superfluous #include qemu/atomic.h

When commit 5f7d05ecfda added QLIST_INSERT_HEAD_RCU() to qemu/queue.h,
it had to include qemu/atomic.h.  Commit 341774fe6cc removed
QLIST_INSERT_HEAD_RCU() again, but neglected to remove the #include.
Do that now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20190812052359.30071-6-armbru@redhat.com>