Add a flag for calling old ChooserTargetService API & remove flags for Shortcuts.

This flag is temporary, just want to make sure we like the state of the world without these targets as we continue down this path.

Test: manual via adb: adb shell device_config get systemui share_use_service_targets false
Bug: 170144291
Change-Id: I8f1ef4b98e7068ff5ee7dbe12827ec4ec034e126