Fix the construction of ziptype APEX

If payload type of APEX is zip, flattened variant and non-flattened
variant create the same MK rules (it's build error). So only
non-flattened variant case, MK rule is created.
And if a.flattenedConfigValue is true, soong don't mutate variants. So
when a.flattenedConfigValue is true, MK rule should be created.

This CL is a partial revert of 4c047138

Bug: 139716748
Test: m -j com.android.art.host
Change-Id: I37b2fa17e203fb668a0255cda37f10fcfadb3f85