main: remove macOS 12.0 Beta boot firmware options

With macOS 12.0.1 and 12.1 available and Mac Mini HDMI display
intialization in m1n1 there is very little value in keeping the beta
versions.
Apple has stopped signing the beta versions a while ago. This breaks the
current installer flow. The boot policy security mode has to be changed
to reduced security (`bputil -g`) before beta stub installs can be
selected as startup disk.

Signed-off-by: Janne Grunau <[email protected]>

Author: jannau

src/main.py

@@ -35,16 +35,6 @@ class IPSW:
 }
 
 IPSW_VERSIONS = [
-    IPSW("12.0 beta 5",
-         "12.0",
-         "iBoot-7429.30.8.0.4",
-         False,
-         "https://updates.cdn-apple.com/2021SummerSeed/fullrestores/071-80097/9F639C04-F128-4EC9-93D3-2AAE04F8A314/UniversalMac_12.0_21A5304g_Restore.ipsw"),
-    IPSW("12.0 beta 8",
-         "12.0",
-         "iBoot-7429.40.84.181.1",
-         False,
-         "https://updates.cdn-apple.com/2021SummerSeed/fullrestores/002-03830/B8D1658D-A579-4479-BBB1-7CDEAF328303/UniversalMac_12.0_21A5534d_Restore.ipsw"),
     IPSW("12.0.1",
          "12.0",
          "iBoot-7429.41.5",