snippets: refactor comment open/close placement

Explicitly comment out every inactive line instead of trying
to optimize for the fewest number of <!-- --> needed.

Benefits:

*) Uncommenting a single project is now a single line change instead
   of potentially a multi-line comment refactor.

*) Git history is more useful.

*) Makes rebasing open commits easier.

Change-Id: Ibc31fb522a90ed8536f775d0c043ebc01ba8dd21