Can't enqueue Google Maps JS API to WordPress
I suspect the issue is due to the dependency that has been set for googlemaps. Instead of passing in an empty array to specify no dependencies for the script, the array contains a blank string. The dependency can't be satisfied so the script isn't loaded.
Simply replace array('') with array().
wp_register_script('googlemaps', 'https://maps.googleapis.com/maps/api/js?&key=AIzaSyCCyUD3v8kBVRphqG1RYjYcSKBcyC-prKw&callback=initMap', array(), '', true);