Rollback to the legacy way of computing boot image locations.

This fixes JIT-zygote builds (b/146462581). The fix is a workaround:
boot image location is computed from boot image filename instead of
using the pre-computed location from the module dexpreopt config.

Currently parts of the dexpreopt module config use boot image name
that is hard-coded in Makefiles, and other parts use boot image name
that is generated by Soong. This is exacerbated by the fact that
"default" boot image config in JIT-zygote builds consists partly of
the "apex" boot image, and partly of "boot" boot image.

Test: walleye_jitzygote-userdebug builds.

Bug: 146462581
Change-Id: I9a91fc48e54d7d43abec2cb2b5a11e3581db380b