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