Emulator builds: Disable camera service Treble mode for now

Until all backwards-compatibility support is in place, the emulator
targets need to not use the Treble path.

Bug: 32991422
Bug: 32989965
Test: Built aosp_x86_64-eng and verified build.prop has the new key
Change-Id: I72487126b0ec7c7794bb3f57f4b1a649a2ec140b