Switch Bazel's CI config to test on Java 11 platforms only.

This removes our Ubuntu 16.04 and Java 8 support.

RELNOTES: Bazel no longer supports Java 8. From this version on, the minimum required JDK is OpenJDK 11.
PiperOrigin-RevId: 404811395
diff --git a/BUILD b/BUILD
index 31430ed..3f42b44 100644
--- a/BUILD
+++ b/BUILD
@@ -202,7 +202,7 @@
     parents = ["@local_config_platform//:host"],
 )
 
-REMOTE_PLATFORMS = ("rbe_ubuntu1604_java8", "rbe_ubuntu1804_java11")
+REMOTE_PLATFORMS = ("rbe_ubuntu1804_java11",)
 
 [
     platform(