Migrate Log4jInitPerformance to log4j-perf.

  - Part of LOG4J2-761 (no specific sub-task as this one was rather trivial).

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1615465 13f79535-47bb-0310-9956-ffa450edef68