I understood the request/question as to just literally remove the slashes '\' on the $jsonString.

You may do so with str_replace().

$test = '{\"acc\":\"0\",\"alarm\":\"02\",\"batl\":\"6\"...........}';
$removed = str_replace('\\', '', $test);

Checking the result

var_dump($removed);
string(46) "{"acc":"0","alarm":"02","batl":"6"...........}" // the output

The output is still a string.