iter 22b.3.2: fix — drop speculative Float (plan-text overreach)

Float is referenced nowhere else in the codebase; the plan-text
listed it aspirationally. Restored parity with the four other
primitive enumerations across the crate. When Float lands as a
real type (post-22b.4 Prelude work, if at all), the arm gets
re-added in the same iter that introduces Type::float().

Deferred (not part of this fix):
- Shared-constant extraction across the four primitive enumeration
  sites (linearity.rs:143, lib.rs:1232/2214, mono.rs) — workspace-
  level cleanup belonging to the milestone-22 audit phase.
- pub mod mono vs sibling pub use lift::lift_letrecs style — plan
  prescribed pub mod for 22b.3 because Tasks 3-7 add multiple pub
  items reached by integration tests; per-item pub use would
  proliferate.

crates/ailang-check/src/mono.rs

@@ -89,8 +89,8 @@ fn workspace_has_typeclasses(ws: &Workspace) -> bool {
 }
 
 /// Iter 22b.3: deterministic mono-symbol name for a `(method,
-/// type)` pair. Primitive types (`Int`, `Bool`, `Str`, `Float`,
+/// type)` pair. Primitive types (`Int`, `Bool`, `Str`, `Unit`)
-/// `Unit`) produce `<method>#<surface-name>` for diagnostic and
+/// produce `<method>#<surface-name>` for diagnostic and
 /// ABI legibility. All other types — parameterised cons,
 /// user-defined ADTs, function types — fall to
 /// `<method>#<8-hex-prefix-of-canonical-type-hash>`. The hash
@@ -123,7 +123,6 @@ fn primitive_surface_name(ty: &Type) -> Option<&'static str> {
             "Int" => Some("Int"),
             "Bool" => Some("Bool"),
             "Str" => Some("Str"),
-            "Float" => Some("Float"),
             "Unit" => Some("Unit"),
             _ => None,
         },