Simplify SQL error handling (#2415)

* Remove sql::error submodule

Use anyhow errors instead.

* Remove explicit checks for open SQL connection

An error will be thrown anyway during attempt to execute query.

* Don't use `with_conn()` and remove it

* Remove unused `with_conn_async`

* Resultify markseen_msgs

src/contact.rs

@@ -175,7 +175,7 @@ pub enum VerifiedStatus {
 }
 
 impl Contact {
-    pub async fn load_from_db(context: &Context, contact_id: u32) -> crate::sql::Result<Self> {
+    pub async fn load_from_db(context: &Context, contact_id: u32) -> Result<Self> {
         let mut contact = context
             .sql
             .query_row(
@@ -915,7 +915,7 @@ impl Contact {
                 }
                 Err(err) => {
                     error!(context, "delete_contact {} failed ({})", contact_id, err);
-                    return Err(err.into());
+                    return Err(err);
                 }
             }
         }