README.md: drop mention of VirtIO Block Media in macOS docs

The previous commit removes our usage of VirtIO Block Media as a backing for the macOS hard disk. We therefore need to drop our descriptions of this functionality now we're not using it any more.

README.md

@@ -351,8 +351,6 @@ macos_release="catalina"
     particular macOS release.
     -   For example VirtIO Network and Memory Ballooning are available
         in Big Sur and newer, but not previous releases.
-    -   And VirtIO Block Media (disks) are supported/stable in Catalina
-        and newer.
 
 ### macOS compatibility
 
@@ -370,9 +368,6 @@ There are some considerations when running macOS via Quickemu.
 -   Optimised by default, but no GPU acceleration is available.
     -   Host CPU vendor is detected and guest CPU is optimised
         accordingly.
-    -   [VirtIO Block
-        Media](https://www.kraxel.org/blog/2019/06/macos-qemu-guest/) is
-        used for the system disk where supported.
     -   [VirtIO `usb-tablet`](http://philjordan.eu/osx-virt/) is used
         for the mouse.
     -   VirtIO Network (`virtio-net`) is supported and enabled on macOS