Fix missing variation error in addDependenciesOntoSelectedBootImageApexes

addDependenciesOntoSelectedBootImageApexes was failing with missing
variant errors when prebuilt tools like dex2oat are added to the apex
contributions contents.  Put back the OtherModuleDependencyVariantExists
check that was remvoed in I1a92ff461d4706cf68a0b8b37e53dea412efb8bf.

Test: m nothing
Bug: 380084017
Change-Id: I2e77e21cc4193b99ce525d17ea321f8c6d426b66