meson: convert dummy Windows qga/qemu-ga target

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -450,11 +450,6 @@ qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx $(SRC_PATH)/scripts/hxtool
 qemu-keymap$(EXESUF): LIBS += $(XKBCOMMON_LIBS)
 qemu-keymap$(EXESUF): QEMU_CFLAGS += $(XKBCOMMON_CFLAGS)
 
-ifneq ($(EXESUF),)
-.PHONY: qga/qemu-ga
-qga/qemu-ga: qga/qemu-ga$(EXESUF) $(QGA_VSS_PROVIDER) $(QEMU_GA_MSI)
-endif
-
 module_block.h: $(SRC_PATH)/scripts/modules/module_block.py config-host.mak
 	$(call quiet-command,$(PYTHON) $< $@ \
 	$(addprefix $(SRC_PATH)/,$(patsubst %.mo,%.c,$(block-obj-m))), \