ZOOKEEPER-2672: Remove CHANGE.txt
ZOOKEEPER-2672: Remove CHANGE.txt

The CHANGE.txt is already not the source of truth of what's changed after we migrating to git - most of the git commits in recent couple of months don't update CHANGE.txt. The option of updating CHANGE.txt during commit flow automatically is none trivial, and do that manually is cumbersome and error prone.
The consensus is we would rely on source control revision logs instead of CHANGE.txt moving forward; see https://www.mail-archive.com/devzookeeper.apache.org/msg37108.html for more details.

Target branches: master, 3.5, 3.4.

Author: Michael Han <hanm@apache.org>

Reviewers: Edward Ribeiro <edward.ribeiro@gmail.com>, Flavio Junqueira <fpj@apache.org>, Rakesh Radhakrishnan <rakeshr@apache.org>

Closes #154 from hanm/ZOOKEEPER-2672

kfirlevari/zookeeper,Obsidian-StudiosInc/zookeeper,Obsidian-StudiosInc/zookeeper,pedrohrf/ZookeeperQuasarFibers,kfirlevari/zookeeper,kfirlevari/zookeeper,ralgond/paxoskeeper,maoling/zookeeper,arshadmohammad/zookeeper,apache/zookeeper,maoling/zookeeper,ralgond/paxoskeeper,apache/zookeeper,maoling/zookeeper,apache/zookeeper,JiangJiafu/zookeeper,pedrohrf/ZookeeperQuasarFibers,arshadmohammad/zookeeper,Obsidian-StudiosInc/zookeeper,JiangJiafu/zookeeper,maoling/zookeeper,pedrohrf/ZookeeperQuasarFibers,apache/zookeeper,ralgond/paxoskeeper,ralgond/paxoskeeper,arshadmohammad/zookeeper,apache/zookeeper,JiangJiafu/zookeeper,hanm/zookeeper,apache/zookeeper,JiangJiafu/zookeeper,maoling/zookeeper,kfirlevari/zookeeper,ralgond/paxoskeeper,Obsidian-StudiosInc/zookeeper,JiangJiafu/zookeeper,hanm/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,Obsidian-StudiosInc/zookeeper,JiangJiafu/zookeeper,Obsidian-StudiosInc/zookeeper,arshadmohammad/zookeeper,Obsidian-StudiosInc/zookeeper,kfirlevari/zookeeper,hanm/zookeeper,kfirlevari/zookeeper,maoling/zookeeper,ralgond/paxoskeeper,JiangJiafu/zookeeper,kfirlevari/zookeeper,ralgond/paxoskeeper,hanm/zookeeper,ralgond/paxoskeeper,hanm/zookeeper,JiangJiafu/zookeeper,hanm/zookeeper,pedrohrf/ZookeeperQuasarFibers,kfirlevari/zookeeper,Obsidian-StudiosInc/zookeeper,maoling/zookeeper,pedrohrf/ZookeeperQuasarFibers,maoling/zookeeper,apache/zookeeper,pedrohrf/ZookeeperQuasarFibers,JiangJiafu/zookeeper,hanm/zookeeper,pedrohrf/ZookeeperQuasarFibers,apache/zookeeper,ralgond/paxoskeeper,arshadmohammad/zookeeper,kfirlevari/zookeeper,pedrohrf/ZookeeperQuasarFibers,Obsidian-StudiosInc/zookeeper,arshadmohammad/zookeeper,hanm/zookeeper,pedrohrf/ZookeeperQuasarFibers