Converting JSON to select list options
The easiest way to do it would be to iterate through the array

$options = array();
foreach($project as $option_group)
{
   $options[key($option_group)] = next($option_group);
}


Or, if you can't count on there being only one element in each option group, do:

$options = array();
foreach($project as $option_group)
{
   $options = array_merge($options, $option_group);
}