[server] Remove pseudo-handling of exceptions in Repository._delete_cascade_multi() It seems to me that we never want to pass on an exception here be it in "test" mode or not, so remove the last `except Exception:` clause. For instance, the actual implementation would pass on an IntegrityError and thus possibly hide it in a log message. Concerning the `except Unauthorized:`, as said by the log message this should not happen because we are within a `security_enabled(write=False)` context. So remove it as well. As far as I can tell, this strange handling of exceptions dates from 37668bf302f5 and there is no clear justification to it.

### Requirements for tests in various cubicweb/**/test directories. ###

## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest

## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag

## cubicweb/devtools/test
flake8

## cubicweb/hooks/test
psycopg2

## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth

## cubicweb/sobject/test
cubicweb-comment