Correcting sub module URLs

Fixed the following:-
1. Removed the unused ceph-object-corpus module
2. Updated the CivetWeb sub module URL, it was using incorrect git URL, changed it to use Https URL
3. Updated the libs3 sub module URL, it was using incorrect git URL, changed it to use Https URL.
4. Updated the rockdb sub module URL, it was using incorrect git URL, changed it to use Https URL. 

This was causing the 'git module update --init' to fails which in fact was called in autogen.sh script. The documented way of creating development environment was failing.