You can try to put it in an external file, but you will not have the possibility to use any of Joomla's feature in it ( like translation of the text or dynamic URLs ).
You can find the javascript code in this file : components\com_aicontactsafe\includes\js\aicontactsafe.js.php .

Basically you need to remove all the php code in that file, replace the php code with appropriate values and generate a new .js file.
Then modify that file to include the new .js file instead of that script.
You need some php and javascript knowledge to do this.

That code is required for the contact form to work.
Without it a lot of the features of the extension will not function.