Revert "Default to building with OpenJDK 9 -target 1.8."

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 original change topic,
https://r.android.com/#/q/topic:bug_69449021

Bug: 69449021
Test: Treehugger

This reverts commit 3337fbfa6114379f13a35ad3d6bf9cb5a5b8689b

Change-Id: Ibc050ad9a87dceb336e7cd961015e70a639e43db