Fix purge-chain and print DB info on startup (#5840)

* purge-chain accepts --db option

* print DB info on startup

* Small refactoring

* Added back &self

* Add DatabaseParams for PurgeChain, ImportParams and ExportBlocks

* Don't force default value

* Remove unused fields

* Update client/cli/src/commands/export_blocks_cmd.rs

* Fix stuff

Co-authored-by: Cecile Tonglet <cecile@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/cli/src/params/shared_params.rs

@@ -14,10 +14,8 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-use sc_service::config::DatabaseConfig;
 use std::path::PathBuf;
 use structopt::StructOpt;
-use crate::arg_enums::Database;
 
 /// Shared parameters used by all `CoreParams`.
 #[derive(Debug, StructOpt, Clone)]
@@ -72,27 +70,6 @@ impl SharedParams {
 		}
 	}
 
-	/// Get the database configuration object for the parameters provided
-	pub fn database_config(
-		&self,
-		base_path: &PathBuf,
-		cache_size: usize,
-		database: Database,
-	) -> DatabaseConfig {
-		match database {
-			Database::RocksDb => DatabaseConfig::RocksDb {
-				path: base_path.join("db"),
-				cache_size,
-			},
-			Database::SubDb => DatabaseConfig::SubDb {
-				path: base_path.join("subdb"),
-			},
-			Database::ParityDb => DatabaseConfig::ParityDb {
-				path: base_path.join("paritydb"),
-			},
-		}
-	}
-
 	/// Get the filters for the logging
 	pub fn log_filters(&self) -> Option<String> {
 		self.log.clone()