Revert exception raising until more confidence in registration system exists.

Having spoken to @mihostet late last year about it, I have reverted the automatic raising of exceptions when registering a new package with cmmnbuild-dep-manager.

This will ease the changes in the next release (v2.3.0) which I plan to release over the coming days (in order to fix the issue with incorrectly determining whether cbng-web is available.