Remove host boot image from boot.zip.

Host boot image is not needed in boot.zip, which is used for the ART
APK scanner and runs on target. This commit also changes the paths in
the boot.zip by removing OS subdirectory.

Test: lunch aosp_cf_x86_phone-userdebug && m
Test: m out/soong/vsoc_x86/dex_bootjars/boot.zip \
    && zipinfo -1 out/soong/vsoc_x86/dex_bootjars/boot.zip
    system/framework/x86/boot-framework.art
    system/framework/x86/boot-framework.oat
    system/framework/x86/boot-ext.art
    system/framework/x86/boot-ext.oat
    system/framework/x86/boot-core-icu4j.art
    system/framework/x86/boot-core-icu4j.oat
    system/framework/x86/boot-telephony-common.art
    system/framework/x86/boot-telephony-common.oat
    system/framework/x86/boot-voip-common.art
    system/framework/x86/boot-voip-common.oat
    system/framework/x86/boot-ims-common.art
    system/framework/x86/boot-ims-common.oat
    system/framework/x86/boot-framework-atb-backward-compatibility.art
    system/framework/x86/boot-framework-atb-backward-compatibility.oat
    system/framework/x86/boot-framework.vdex
    system/framework/x86/boot-ext.vdex
    system/framework/x86/boot-core-icu4j.vdex
    system/framework/x86/boot-telephony-common.vdex
    system/framework/x86/boot-voip-common.vdex
    system/framework/x86/boot-ims-common.vdex
    system/framework/x86/boot-framework-atb-backward-compatibility.vdex

Change-Id: Idf0541908059c454348181d90b0b3e5d6d350057