Remove evidence of kitrap0d

This exploit has been causing crashes and BSODs on various systems and
hence is deemed too unstable to be included in the default deployment of
Meterpreter. `getsystem` should only contain code which attempts to get
SYSTEM privileges via safe means; it should not have exploits in it.

This commit removes kitrap0d from `getsystem`. The code will be moved to a
windows local exploit in MSF instead.
Land #51, @OJ deletion of kitrap0d from getsystem