d/control: Switch priority to optional

Otherwise the laptop installer breaks

debian/control

@@ -13,7 +13,7 @@ Homepage: https://source.puri.sm/Librem5/librem5-base
 
 Package: librem5-base
 Architecture: all
-Priority: important
+Priority: optional
 Depends:
  librem5-base-defaults (>= ${source:Version}),
  ${germinate:Depends},
@@ -30,7 +30,7 @@ Description: Metapackage for the Librem5
 
 Package: librem5-gnome-base
 Architecture: all
-Priority: important
+Priority: optional
 Depends:
  librem5-base (>= ${source:Version}),
  ${germinate:Depends},