hw/misc/sga: Remove the deprecated "sga" device

It's been deprecated since QEMU v6.2, so it should be OK to
finally remove this now.

Message-Id: <20230209161540.1054669-1-thuth@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

.gitmodules

@@ -13,9 +13,6 @@
 [submodule "roms/qemu-palcode"]
 	path = roms/qemu-palcode
 	url = https://gitlab.com/qemu-project/qemu-palcode.git
-[submodule "roms/sgabios"]
-	path = roms/sgabios
-	url = https://gitlab.com/qemu-project/sgabios.git
 [submodule "dtc"]
 	path = dtc
 	url = https://gitlab.com/qemu-project/dtc.git