Remove useless provider setting for connection url based domain settings

Author: alex-kulakov

Orm/Xtensive.Orm.Tests.Framework/Orm.config

@@ -66,10 +66,10 @@
     <domain name="mysql56"
             connectionUrl="mysql://dotest:dotest@localhost:3356/dotest" />
 
-    <domain name="firebird25" provider="firebird"
+    <domain name="firebird25"
             connectionUrl="firebird://dotest:dotest@localhost:3050/dotest" />
 
-    <domain name="firebird30" provider="firebird"
+    <domain name="firebird30"
         connectionUrl="firebird://dotest:dotest@localhost:3053/dotest" />
 
     <domain name="sqlite3"