php - Skip Submit button in array_keys

I've got a PHP routine that processes a form and outputs the values
to a CSV file. I'm using array_keys() to create the header row
(skipped if there is one). Everything works perfectly except the final header term is
"submit" because, of course, my form includes a Submit button. So the data ends up
looking like
this:

name,email,cell,dob,study,submit
"Temp
            One",fred@gmail.com,646-325-1111,1995-03-31,8,Submit
"Temp
            Two",tom@gmail.com,646-325-2222,1995-03-31,4,Submit

How
do I omit the submit button both from the header and the
data?

Here's my
code:

if(isset($_POST['submit']))
            {
 $data = array_values($_POST); // get only values
 $headers =
            array_keys($_POST); // keys are headers 
 if( $fp = fopen('data.csv','a+'))
            {
 $line = fgets($fp);
 if(!$line == $headers) {

            fputcsv($fp, $headers);
 fputcsv($fp, $data);
 }

            else

 {
 fputcsv($fp, $data);
 }

            fclose($fp);
 header('Location: thanks.php'); 

            }
}

class="post-text" itemprop="text">

class="normal">Answer

Remove it
from the array...

$post
            = $_POST;
unset($post['submit']);
$data = array_values($post); //
            get only values
$headers = array_keys($post); // keys are headers