all: remove support for stage1

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

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

gamemode.zig

@@ -1,10 +1,7 @@
 //! Note: All the above requests can be blocking - dbus requests can and will block while the daemon
 //! handles the request. It is not recommended to make these calls in performance critical code
 const builtin = @import("builtin");
-pub const c = if (builtin.zig_backend == .stage1)
-    @import("gamemode_client_stage1.zig")
-else
-    @import("gamemode_client.zig");
+pub const c = @import("gamemode_client.zig");
 
 pub const GamemodeError = error{
     RequestFailed,