Revert "Add product and system_ext partition for emulator"

This reverts commit ef7e3f26.

The configuration affects GSI to have separate partitions for product
and system_ext which was not intended.

Bug: 138742524
Bug: 138382074
Test: emulator; check boot
Change-Id: Ie621d6b49f22ee2775adf1c1497e812f840f8ba7