package.bbclass: Drop EXPORT_FUNCTIONS use against mapping_rename_hook
The usage of this function renaming and it being called using
bb.build.exec_func() causes needless indirection loops, confusing log
files and seems generally pointless.
This simplification makes the process much simpler and faster. I can't
come up with a good reason why the export_functions functionality is
needed for this function.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
