install.php file was placed on the server 8/3/2018. So, either GoDaddy put it there or it was added by a plugin. My vote is on GoDaddy based on that support thread I found and shared with you.
This file is not part of the standard WordPress install. It is used solely for the purpose to run custom functions on installation of WP and should be removed afterward. You can learn more about this file here.
Whatever added this file, it can not be deleted, downloaded or have its permissions changed (at least thru a FTP program like Filezilla). These actions simply error, permission denied.
Now, it can be renamed. So that is what I did. I added
.old to the filename. Now Connections was able to be activated. The other plugins should activate fine too, but I did not try as it did not seem necessary.
Whatever this file is doing, it can not be much, judging based on its file size.
Hope this helps!