ui/Makefile.objs: delete unnecessary cocoa.o dependency

Delete an unnecessary dependency for cocoa.o; we already have
a general rule that tells Make that we can build a .o file
from a .m source using an ObjC compiler, so this specific
rule is unnecessary. Further, it is using the dubious construct
"$(SRC_PATH)/$(obj)" to get at the source directory, which will
break when $(obj) is redefined as part of the preparation for
per-object library support.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

ui/Makefile.objs

@@ -17,6 +17,4 @@ common-obj-$(CONFIG_GTK) += gtk.o x_keymap.o
 
 $(obj)/sdl.o $(obj)/sdl_zoom.o: QEMU_CFLAGS += $(SDL_CFLAGS) 
 
-$(obj)/cocoa.o: $(SRC_PATH)/$(obj)/cocoa.m
-
 $(obj)/gtk.o: QEMU_CFLAGS += $(GTK_CFLAGS) $(VTE_CFLAGS)