docs: process: Remove outdated info about -git patches

As can be seen by clicking around the timeline on web.archive.org[1],
there were no -git patches/tarballs on kernel.org since release 3.1.

[1]: https://web.archive.org/web/20111103073843/http://www.kernel.org/



Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>