don't update to 10.15.5 with EFI 5700

Our friends in Cupertino have broken support for EFI 5700 in 10.15.5.

Stay on 10.15.4 until we get a fix. If your 5700 has a ROM switch and you are on 10.15.5, you can use the PC side to work around for now.

​Will update as we find solution.