oraclejdk: Revert "oraclejdk8: 8u91 -> 8u92" (#15820)

This reverts commit 9e56f3a9.

8u91 is Critical Patch Update (CPU), contains security vulnerability fixes.
8u92 is Patch Set Update (PSU), contains security vulnerability fixes
and other bug fixes.

Oracle says "Oracle strongly recommends that all Java SE users upgrade
to the latest CPU release available for a release family. Most users
should choose the CPU release."
http://www.oracle.com/technetwork/java/javase/downloads/cpu-psu-explained-2331472.html

So I made `oraclejdk8` package and `oraclejdk8psu` package for CPU and PSU.