remove unused memory allocator

src/main.zig

@@ -40,9 +40,6 @@ const Config = struct {
     coin_key: i32,
 };
 
-var gpa = std.heap.GeneralPurposeAllocator(.{}){};
-const alloc = gpa.allocator();
-
 var cfg: ?Config = null;
 var thread_op = std.Thread.Mutex{};
 var slider_active = false;