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/device.zig

@@ -31,18 +31,11 @@ const Impl = @import("interface.zig").Impl;
 const dawn = @import("dawn.zig");
 
 pub const Device = opaque {
-    pub const LostCallback = if (@import("builtin").zig_backend == .stage1)
-        fn (
-            reason: LostReason,
-            message: [*:0]const u8,
-            userdata: ?*anyopaque,
-        ) callconv(.C) void
-    else
-        *const fn (
-            reason: LostReason,
-            message: [*:0]const u8,
-            userdata: ?*anyopaque,
-        ) callconv(.C) void;
+    pub const LostCallback = *const fn (
+        reason: LostReason,
+        message: [*:0]const u8,
+        userdata: ?*anyopaque,
+    ) callconv(.C) void;
 
     pub const LostReason = enum(u32) {
         undef = 0x00000000,