Do not remove player in world change. Fixes BUKKIT-4561 and BUKKIT-4082 

**The Issue:**
The player who is respawning during a PlayerRespawnEvent is not listed on the playerlist during that time.


**The Justification:**

During player respawn and change world within vanilla minecraft, the EntityPlayer is replaced by a new instance of EntityPlayer, however, CraftBukkit once saw fit to not create a new instance, but rather just reuse the same one to prevent many issues that re-instancing would cause with the API.  That decision, whenever it was made, made the removal of the old EntityPlayer and addition of the new EntityPlayer unnecessary.  It has also been found that not only are those two actions not neccessary, but they are also breaking to the PlayerRespawnEvent,  breaking methods such as .getPlayer()  and its variations,   .getOnlinePlayers()   and any Scoreboard API method that necessitates packets being sent to the player, as the player respawning does not receive said packets, and therefore crashes when the next scoreboard change is sent to them.

**PR Breakdown:**

This commit removes the unnecessary and API breaking code to prevent these problems.

**Example Scoreboard API code that did not work previously but will now (And associated errors that occured before):**

http://pastebin.com/Pg6AxpA4

**Testing for breakage:**
In the weeks since I found this bug, I have tested every player API method, every API method that results in packets being sent to a player, and many other API methods just in case. 

**JIRA Tickets:**
https://bukkit.atlassian.net/browse/BUKKIT-4561

https://bukkit.atlassian.net/browse/BUKKIT-4082