Begin removing the MyError type.

src/context/context.rs

@@ -9,7 +9,6 @@ use super::list::List;
 use super::DynContextMatcher;
 use super::RefContext;
 use crate::error::CustomError;
-use crate::error::MyError;
 use crate::error::Res;
 use crate::parser::OrgSource;