function charsEndIndex(strSymbols, chrSymbols) {
	    var index = strSymbols.length;
	
	    while (index-- && baseIndexOf(chrSymbols, strSymbols[index], 0) > -1) {}
	    return index;
	  }
Used by `_.deburr` to convert Latin-1 Supplement and Latin Extended-A
letters to basic Latin letters.

@private
@param {string} letter The matched letter to deburr.
@returns {string} Returns the deburred letter.