Remove repeating character

How would I remove repeating characters (e.g. remove the letter k in cakkkke for it to be cake)?

One straightforward way to do this would be to loop through each character of the string and append each character of the string to a new string if the character isn't a repeat of the previous character.

Here is some code that can do this:

$newString = '';
$oldString = 'cakkkke';
$lastCharacter = '';
for ($i = 0; $i < strlen($oldString); $i++) {
    if ($oldString[$i] !== $lastCharacter) {
        $newString .= $oldString[$i];
    }
    $lastCharacter = $oldString[$i];
}
echo $newString;

Is there a way to do the same thing more concisely using regex or built-in functions?