Don't check PRODUCT_SHIPPING_API_LEVEL to determine fake treble.

Emulator device can not be considered a full treble device even though
it has PRODUCT_SHIPPING_API_LEVEL = 28. This is prevents us from merging
neverallow rules that implement Treble requirements (aosp/798433). As a
temporary workaround, disable the checks on that variable.

Bug: 112933807
Bug: 113124961
Bug: 111243627
Test: m selinux_policy
Change-Id: I9a29c01dfcbc70e4ba1e4eef233355bc18ec2108