Remove the file extname associated processors.

@inner
@param {string|Array.<string>} extnames the file extnames
@param {string} processorName the processor name
@param {Object} existedMap the existed file extname associated processors map
function removeFileExtnameAssociatedProcessor(extnames, processorName, existedMap) {
    if (!extnames) {
        return;
    }

    if (!Array.isArray(extnames)) {
        extnames = [extnames];
    }

    extnames.forEach(k => {
        let currItems = existedMap[k];
        if (Array.isArray(currItems)) {
            let idx = currItems.indexOf(processorName);
            if (idx !== -1) {
                currItems.splice(idx, 1);
                currItems.length === 0 && (existedMap[k] = undefined);
            }
        }
        else if (currItems === processorName) {
            existedMap[k] = undefined;
        }
    });
}