ZOOKEEPER-2083: Remove deprecated class AuthFastLeaderElection

As per [ZOOKEEPER-2083](https://jira.apache.org/jira/browse/ZOOKEEPER-2083) we need to remove class AuthFastLeaderElection.java so I made changes in Quorumpeer.java by removing two cases 1 and 2 present in createElectionAlgorithm as QuorumPeerconfig.electioalg is always 3.

Please do let me know if anything additional needs to be done.

Author: ravowlga123 <ravowlga@gmail.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Andor Molnar <anmolnar@apache.org>, Patrick Hunt <phunt@apache.org>

Closes apache#1171 from ravowlga123/ZOOKEEPER-2083

zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md

@@ -1146,12 +1146,13 @@ of servers -- that is, when deploying clusters of servers.
     non-authenticated UDP-based version of fast leader election, "2"
     corresponds to the authenticated UDP-based version of fast
     leader election, and "3" corresponds to TCP-based version of
-    fast leader election. Currently, algorithm 3 is the default.
+    fast leader election. Algorithm 3 was made default in 3.2.0 and 
+    prior versions (3.0.0 and 3.1.0) were using algorithm 1 and 2 as well.
     ###### Note
-    >The implementations of leader election 1, and 2 are now
-    **deprecated**. We have the intention
-    of removing them in the next release, at which point only the
-    FastLeaderElection will be available.
+    >The implementations of leader election 1, and 2 were 
+    **deprecated** in 3.4.0. Since 3.6.0 only FastLeaderElection is available, 
+    in case of upgrade you have to shutdown all of your servers and 
+    restart them with electionAlg=3 (or by removing the line from the configuration file).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        >                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
 
 * *maxTimeToWaitForEpoch* :
   (Java system property: **zookeeper.leader.maxTimeToWaitForEpoch**)