[posix-sim] remove unused variable (#4103)
[posix-sim] remove unused variable (#4103)


turon/openthread,jwhui/openthread,openthread/openthread,chshu/openthread,openthread/openthread,lanyuwen/openthread,lanyuwen/openthread,chshu/openthread,srickardti/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,lanyuwen/openthread,librasungirl/openthread,turon/openthread,librasungirl/openthread,turon/openthread,bukepo/openthread,chshu/openthread,jwhui/openthread,abtink/openthread,librasungirl/openthread,chshu/openthread,abtink/openthread,bukepo/openthread,srickardti/openthread,jwhui/openthread,turon/openthread,jwhui/openthread,librasungirl/openthread,lanyuwen/openthread,bukepo/openthread,srickardti/openthread,abtink/openthread,chshu/openthread,chshu/openthread,lanyuwen/openthread,openthread/openthread,openthread/openthread,bukepo/openthread