Remove obex library code from frameworks/base.

The obex library has been migrated to platform/external/obex as it uses
the BSD license and should not be in any non-3p repo. Only the ObexPacket
class is retained as it is a public API.

Bug: 219056000
Bug: 220211554
Test: Manual
Change-Id: If279fda41b7790abe0f25d9ebd8ea4c6fb58cbbb
diff --git a/obex/Android.bp b/obex/Android.bp
index 37e7f76..d89d41d 100644
--- a/obex/Android.bp
+++ b/obex/Android.bp
@@ -44,6 +44,8 @@
     ],
 }
 
+// No longer used. Only kept because the ObexPacket class is a public API.
+// The library has been migrated to platform/external/obex.
 java_sdk_library {
     name: "javax.obex",
     srcs: ["javax/**/*.java"],