Remove equal overriden groups attributes

===

<svg xmlns="http://www.w3.org/2000/svg">
    <g attr1="val1">
        <g attr2="val2">
            <path attr2="val2" d="..."/>
        </g>
        <g attr2="val2">
            <path attr2="val3" d="..."/>
        </g>
    </g>
</svg>

@@@

<svg xmlns="http://www.w3.org/2000/svg">
    <g attr1="val1">
        <path attr2="val2" d="..."/>
        <g attr2="val2">
            <path attr2="val3" d="..."/>
        </g>
    </g>
</svg>