Remove concat expression (#5183)

It's not a scalar expression

Signed-off-by: Nicholas Gates <nick@nickgates.com>

Author: gatesn

vortex-expr/src/exprs/concat.rs

@@ -4,7 +4,6 @@
 pub(crate) mod between;
 pub(crate) mod binary;
 pub(crate) mod cast;
-pub(crate) mod concat;
 pub mod dynamic;
 pub(crate) mod get_item;
 pub(crate) mod is_null;

vortex-expr/src/exprs/mod.rs

@@ -39,7 +39,6 @@ pub use analysis::*;
 pub use between::*;
 pub use binary::*;
 pub use cast::*;
-pub use concat::*;
 pub use encoding::*;
 pub use get_item::*;
 pub use is_null::*;