all: remove support for stage1

With almost all tests/examples working on all platforms now with the new compiler,
https://github.com/hexops/mach/issues/180, it's time to remove stage1 support.

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

libs/gpu/src/queue.zig

@@ -9,16 +9,10 @@ const CopyTextureForBrowserOptions = @import("types.zig").CopyTextureForBrowserO
 const Impl = @import("interface.zig").Impl;
 
 pub const Queue = opaque {
-    pub const WorkDoneCallback = if (@import("builtin").zig_backend == .stage1)
-        fn (
-            status: WorkDoneStatus,
-            userdata: ?*anyopaque,
-        ) callconv(.C) void
-    else
-        *const fn (
-            status: WorkDoneStatus,
-            userdata: ?*anyopaque,
-        ) callconv(.C) void;
+    pub const WorkDoneCallback = *const fn (
+        status: WorkDoneStatus,
+        userdata: ?*anyopaque,
+    ) callconv(.C) void;
 
     pub const WorkDoneStatus = enum(u32) {
         success = 0x00000000,