healthd: add stem to health@2.0-service.override [DO NOT MERGE]

The override module should have the same name as the -service
module; the only difference is that healthd is installed or not.
Without this change, the binary is completely useless due to
incorrect rc files and sepolicy file_contexts.

This allows emulator to use this module correctly.

Bug: 110228707

Test: builds on emulator, boots
Change-Id: Id2062925ec3567c4fde70358184bb790541bf83b