because in dataguard we do not need to run any scripts which touches STANDBY database.
You cant uninstall/remove patchset from the binaries..You have to restore the 10.2.0.4 home from the backup
It is not possible to uninstall a patchset. Either Oracle home needs to be restored from Oracle home or install it again. Once done, you may simply enable log shipping and it should take care of standby database.
334598.1 - How To Rollback A Patchset