Feature cleanup (#7182)

Following up on #7180 with some feature cleanup:

- Move the `database` feature from `plugin` to `default`
- Rename the `database` feature to `sqlite`
- Remove `--features=extra` from a lot of scripts etc. 
- No need to specify this, the `extra` feature is now the same as the
default feature set
- Remove the now-redundant 2nd Ubuntu test run

tests/plugins/custom_values.rs

@@ -53,7 +53,7 @@ fn can_get_describe_plugin_custom_values() {
 // There are currently no custom values defined by the engine that aren't hidden behind an extra
 // feature, both database and dataframes are hidden behind --features=extra so we need to guard
 // this test
-#[cfg(feature = "database")]
+#[cfg(feature = "sqlite")]
 #[test]
 fn fails_if_passing_engine_custom_values_to_plugins() {
     let actual = nu_with_plugins!(