Build java.obex with java_sdk_library

javax.obex is built with java_sdk_library and api files are added by
running "make update-api".
Remove java.obex is from platform.xml, since it will be generated
automatically by soong when the library is built with java_sdk_library.

Bug:77577799
Test: make -j
      make checkapi

Change-Id: Ib94955e62582ffbdfc7eb88cd0e494c61757c7aa

obex/api/current.txt

@@ -0,0 +1,12 @@
+package javax.obex {
+
+  public class ObexPacket {
+    method public static javax.obex.ObexPacket read(java.io.InputStream) throws java.io.IOException;
+    method public static javax.obex.ObexPacket read(int, java.io.InputStream) throws java.io.IOException;
+    field public int mHeaderId;
+    field public int mLength;
+    field public byte[] mPayload;
+  }
+
+}
+