Removing --flag 2 when building GSI vbmeta.img

With the support of enabling AVB on standalone partitions in libfs_avb,
devices can boot GSI with dm-verity. No need to disable AVB anymore.

Devices still can use the following command to disable AVB on
device-specific vbmeta.img if needed:

    `fastboot flash --disable-verification vbmeta vbmeta.img`

Bug: 130595457
Test: Tree Hugger
Change-Id: I067dcda15f14f04428e0b60ce1f49227d61e4349
diff --git a/target/board/BoardConfigGsiCommon.mk b/target/board/BoardConfigGsiCommon.mk
index d4025c3..96fd07b 100644
--- a/target/board/BoardConfigGsiCommon.mk
+++ b/target/board/BoardConfigGsiCommon.mk
@@ -28,16 +28,9 @@
 BOARD_USES_METADATA_PARTITION := true
 
 # Android Verified Boot (AVB):
-#   Set AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED (--flags 2) in
-#   vbmeta.img to disable AVB verification. Also set the rollback index
-#   to zero, to prevent the device bootloader from updating the last seen
-#   rollback index in the tamper-evident storage.
-#
-# To disable AVB for GSI, use the vbmeta.img and the GSI together.
-# To enable AVB for GSI, include the GSI public key into the device-specific
-# vbmeta.img.
+#   Set the rollback index to zero, to prevent the device bootloader from
+#   updating the last seen rollback index in the tamper-evident storage.
 BOARD_AVB_ROLLBACK_INDEX := 0
-BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 2
 
 # Enable chain partition for system.
 BOARD_AVB_SYSTEM_KEY_PATH := external/avb/test/data/testkey_rsa2048.pem