chore(proxy): remove enum and composite type queries (#11178)

In our json encoding, we only need to know about array types.
Information about composites or enums are not actually used.

Enums are quite popular, needing to type query them when not needed can
add some latency cost for no gain.

libs/proxy/postgres-types2/src/lib.rs

@@ -135,8 +135,8 @@ impl Type {
 pub enum Kind {
     /// A simple type like `VARCHAR` or `INTEGER`.
     Simple,
-    /// An enumerated type along with its variants.
-    Enum(Vec<String>),
+    /// An enumerated type.
+    Enum,
     /// A pseudo-type.
     Pseudo,
     /// An array type along with the type of its elements.
@@ -146,9 +146,9 @@ pub enum Kind {
     /// A multirange type along with the type of its elements.
     Multirange(Type),
     /// A domain type along with its underlying type.
-    Domain(Type),
-    /// A composite type along with information about its fields.
-    Composite(Vec<Field>),
+    Domain(Oid),
+    /// A composite type.
+    Composite(Oid),
 }
 
 /// Information about a field of a composite type.