Removing 1.9 as fixed target for libcore libraries

The default option in Android now is to use Java 1.9, so the
java_version option in libcore is not needed anymore.
Furthermore, it's better to not have it defined to allow the
build system to target for a newer version (like Java 11).

Bug: 195387473
Test: m
Test: EXPERIMENTAL_TARGET_JAVA_VERSION_11=true m
Change-Id: Ib016270288545bb9403dee6cc29f23036e3b0ef3
1 file changed