remove ion button padding

You need to set the no-padding attribute on ion-col instead of ion-row and no-margin for the buttons.

<ion-row>
    <ion-col col-6 no-padding>
        <button ion-button full no-margin>Button</button>
    </ion-col>
    <ion-col col-6 no-padding>
        <button ion-button full no-margin>Button</button>
    </ion-col>
</ion-row>