healthd use vintf_fragments

This encourages device manufacturers to use
service.override over service and to remove healthd
on device, because it is one less step to do.

Test: make VINTF metadata
Bug: 66917623
Change-Id: I447395450060cdf17731514bb9a5e3ed912bbc66
Merged-In: I447395450060cdf17731514bb9a5e3ed912bbc66
(cherry picked from commit ae005c46)