Install apex symlinks in m --soong-only

Apexes such as com.android.runtime install additional symlinks in the
staging $PRODUCT_OUT/apex directory. It uses
PathForModuleInPartition("apex") to avoid the side affect of
inadvertently copying this into rdeps such as system.img

To prevent non-null builds when switching between `m` and `m
--soong-only`, remove this special case.

Test: m nothing
Bug: 390471378
Change-Id: I81ff7b9c18f84cbe83836e6992124080c93359d2