cpu-defs.h: Drop qemu_work_item prototype

Commit c64ca8140e9c21cd0d44c10fbe1247cb4ade8e6e (cpu: Move
queued_work_{first,last} to CPUState) moved the qemu_work_item fields
away. Clean up the now unused prototype.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

include/exec/cpu-defs.h

diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
index d0cf85a..2911b9f 100644
--- a/include/exec/cpu-defs.h
+++ b/include/exec/cpu-defs.h
@@ -134,8 +134,6 @@
 } icount_decr_u16;
 #endif
 
-struct qemu_work_item;
-
 typedef struct CPUBreakpoint {
     target_ulong pc;
     int flags; /* BP_* */