removed dupe ex 057 from build script

build.zig

@@ -297,10 +297,6 @@ const exercises = [_]Exercise{
         .main_file = "057_unions3.zig",
         .output = "Insect report! Ant alive is: true. Bee visited 17 flowers.",
     },
-    .{
-        .main_file = "057_unions3.zig",
-        .output = "Insect report! Ant alive is: true. Bee visited 17 flowers.",
-    },
 };
 
 /// Check the zig version to make sure it can compile the examples properly.