Cleanup of ZygoteServer.java

This patch cleans up ZygoteServer.java:
* Remove unnecessary initialization
* Replaces a lambda with a method references
* Makes several values final
* Removes unnecessary type specifications

Test: m & flash & boot
Change-Id: I26cc7e7ad54dc510ef0abc51a73190cf8e5096d1
Merged-In: I26cc7e7ad54dc510ef0abc51a73190cf8e5096d1
(cherry picked from commit b2b9ce54)