Disable example codec2-service by default

`android.hardware.media.c2@1.1-default-service` is an example codec2
service, developers who wish to implement codec2 can use this code as a
skeleton.
`android.hardware.media.c2@1.1-default-service` is not to be used
directly without customization. Mark it as "enabled: false" so it
wouldn't affect build.

Bug: 159780061
Test: TH
Change-Id: I61f2d50dd9279981fb78af8c1ac76e00f9ad8487