Disable avb for userdata partition

To make the behavior identical between make and soong.

Test: m out/soong/.intermediates/build/soong/fsgen/aosp_cf_x86_64_phone_generated_userdata_image/android_common/userdata.img
Bug: 388920173
Change-Id: I4b89be5c0f5355b63791dde77278217f3a82318e