Remove the given property name style declaration that the position is
front of the current given style declaration.

@inner
@param {Object} decl the style property declaration that will override
the front of the style declaration that has the same property name
@param {string} toRemovePropName the property name to remove
function removeUnUseDecl(decl, toRemovePropName) {
    let nodes = decl.parent.nodes;
    let currIdx = nodes.indexOf(decl);

    for (let i = currIdx - 1; i >= 0; i--) {
        let item = nodes[i];
        if (item.type === 'decl' && item.prop === toRemovePropName) {
            item.remove();
        }
    }
}