Pin jarjar'ed target telephony-protos to java_version 1.8.

This allows the default target java_version to advance before /
independently of jarjar support for higher (v53) class file
versions.

Bug: 72703434
Test: EXPERIMENTAL_USE_OPENJDK9=true USE_R8=true make checkbuild docs
      (in a client where CL http://r.android.com/596874 was reverted)

Change-Id: I10c56ddc6f84691045d2e6e494a26e7c797ba22a
diff --git a/proto/Android.bp b/proto/Android.bp
index 8e24b50..a36f7a5 100644
--- a/proto/Android.bp
+++ b/proto/Android.bp
@@ -24,4 +24,6 @@
     srcs: ["src/**/*.proto"],
     no_framework_libs: true,
     jarjar_rules: "jarjar-rules.txt",
+    // Pin java_version until jarjar is certified to support later versions. http://b/72703434
+    java_version: "1.8",
 }
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