Remove dpranke from OWNERS.

I'm no longer tracking the work in this repo closely enough,
nor am I writing enough C++, to really be a good owner at
this point. Perhaps this will change again at some point in
the future, but for now, considering me an OWNER just seems
like it can confuse people.

Change-Id: I2224027f204c7c61ce71a7e62f0baf335f84b4f9
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/4500
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

OWNERS

@@ -1,4 +1,3 @@
 brettw@chromium.org
-dpranke@chromium.org
 phosek@chromium.org
 scottmg@chromium.org