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

crates/nu-command/src/lib.rs

@@ -62,8 +62,8 @@ mod dataframe;
 #[cfg(feature = "dataframe")]
 pub use dataframe::*;
 
-#[cfg(feature = "database")]
+#[cfg(feature = "sqlite")]
 mod database;
 
-#[cfg(feature = "database")]
+#[cfg(feature = "sqlite")]
 pub use database::*;