Revert "Rename `libsyn` to `libsyn2`"

This reverts commit 7705ea6d369298024f27143ed2424a41f3e07adf.

Reason for revert: I believe this is stale since `libsyn` is version 2 now:

https://cs.android.com/android/platform/superproject/+/main:external/rust/crates/syn/Android.bp;l=41;drc=fcd71dcc29ef325341ea7c1a145591b349018eb3

Change-Id: I31892447cf95d094e4bb201c4d86a28c70085467
1 file changed