Switch to `libjni_legacy`

We're updating `libjni` to `0.21`. This involves several API breakages, so I'm rewriting everyone to use `libjni_legacy` first to allow `libjni` to be upgraded. Follow-up changes will update you to use `libjni`.

Change-Id: Iccff3b4a7a74a370cf175bb6e8b966f70949a180
diff --git a/src/Android.bp b/src/Android.bp
index 54b746e..86c3a21 100755
--- a/src/Android.bp
+++ b/src/Android.bp
@@ -248,7 +248,7 @@
         "libbinder_rs",
         "libbinder_tokio_rs",
         "libbytes",
-        "libjni",
+        "libjni_legacy",
         "liblog_rust",
         "libthiserror",
         "libtokio",