build: remove the special eowyn build mode

The special eowyn mode was added in order to improve the performance of
the Eowyn Github workflow.

Remove it, since it adds unnecessary complexity to the `build.zig` file.

Closes #297

build.zig

@@ -192,29 +192,6 @@ pub fn build(b: *Build) !void {
         start_step.dependOn(&prev_step.step);
 
         return;
-    } else if (healed and false) {
-        // Special case when healed by the eowyn script, where we can make the
-        // code more efficient.
-        //
-        // TODO: this branch is disabled because it prevents the normal case to
-        // be executed.
-        const test_step = b.step("test", "Test the healed exercises");
-        b.default_step = test_step;
-
-        for (exercises) |ex| {
-            const build_step = ex.addExecutable(b, healed_path);
-            b.installArtifact(build_step);
-
-            const run_step = b.addRunArtifact(build_step);
-            if (ex.skip) {
-                const skip_step = SkipStep.create(b, ex);
-                test_step.dependOn(&skip_step.step);
-            } else {
-                test_step.dependOn(&run_step.step);
-            }
-        }
-
-        return;
     }
 
     // Run all exercises in a row