[MERGE] Remove Branch.get_root_id

[John Arbash Meinel]

John Arbash Meinel has voted +1.
Status is now: Approved
Comment:
I agree with you.

This should have a NEWS entry about bug 96847

Also, I would like to wait until we know why James Henstridge wanted to 
use Branch.get_root_id()

(At first I thought 'bzr upgrade' was failing, which meant we needed to 
do more than just deprecate this method. But it seems it is just that it 
fails in both formats)

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C46091C44.6050606%40utoronto.ca%3E