Revert "Build with OpenJDK 9 -target 1.8 by default except for errorprone."

After this revert CL topic, the default toolchain for Android
goes back to being OpenJDK 8.

This revert is being prepared ahead of time in case of
any problems with CL topic:
https://r.android.com/#/q/topic:bug69449021_attempt2

Bug: 69449021
Test: Treehugger

Change-Id: I0ef41eff91e0d8437dc95e8569880f26f2529bc9