[dep-plumbing] getting rid of VCS column in the DEP index

[Charles Plessy]

Dear Stefano and Ben,

as discussed in private earlier, I have transferred VCS information of each DEP
from the index to the DEP itself.

To do so, I created a "Source" field for the DEP headers, that I documented in
DEP 0, which indicates one or more browsable URLs.  I chose to discard the VCS
URLs for checkout, which anyway did not exist for DEPs managed in a wiki, and
are easy to guess from the browsable URLs anyway.

Have a nice Sunday,

-- 
Charles