renderer/vulkan: drop the smoke test harness

`smoke.zig` was the bring-up harness used to validate the Vulkan
device + pipeline plumbing in isolation before the renderer was
wired up end-to-end. The real renderer is now driving every code
path the smoke tests exercised (and then some), so the harness is
dead weight — 1.3 kloc and an env-gated `test {}` block in
Vulkan.zig that only exists to import it.

Removes the file and the corresponding `_ = @import` in
Vulkan.zig's test block (which then becomes empty and goes away
too).

Co-Authored-By: claude-flow <ruv@ruv.net>

src/renderer/Vulkan.zig

@@ -661,16 +661,3 @@ pub fn initAtlasTexture(
     );
 }
 
-test {
-    // Don't `refAllDecls` here — some methods (like `surfaceSize`)
-    // @compileError when `apprt.runtime` is `.none`, which is the
-    // runtime used by `zig build test`. Force-resolving every decl
-    // would trip those errors before tests can run. The OpenGL and
-    // Metal backends sidestep this by not having a `test {}` block
-    // at all.
-    //
-    // We DO want to pull in the smoke test (gated on
-    // `GHOSTTY_VULKAN_SMOKE` env var so it doesn't run resource-
-    // creating tests by default).
-    _ = @import("vulkan/smoke.zig");
-}