Disable sparse filesystems

The filesystems should not be parse unless one of the size-related
variables are set, but currently filesystems don't support setting those
size variables.

Bug: 381120092
Test: m out/soong/.intermediates/build/soong/fsgen/aosp_cf_x86_64_phone_generated_system_image/android_common/aosp_cf_x86_64_phone_generated_system_image.img && file out/soong/.intermediates/build/soong/fsgen/aosp_cf_x86_64_phone_generated_system_image/android_common/aosp_cf_x86_64_phone_generated_system_image.img; observe that the filesystem is erofs instead of android sparse image
Change-Id: I741531d5af8ad85664658995cd9fd3b46533d73c