[DRE-maint] Bug#1027710: libruby3.0: drop Provides: ruby-dbm (now provided separately)

[Drew Parsons]

Package: libruby3.0
Version: 3.0.4-8
Severity: normal

A new ruby-dbm package was recently created to resolve Bug#1027407
(dhelp Depends: ruby-dbm)

But libruby3.0 still declares Provides: ruby-dbm (= 1.1.0)
and so the new ruby-dbm 1.1.0-2 doesn't actually get installed by a
standard upgrade.

I guess libruby3.0 should now drop Provides: ruby-dbm
since it no longer provides dbm.