refactor(poly): updated header guards to pragma once

src/poly/utils/public/operator.h

@@ -1,5 +1,4 @@
-#ifndef POLY_UTILS_OPERATOR_H
-#define POLY_UTILS_OPERATOR_H
+#pragma once
 
 #include "mfem.hpp"
 #include "4DSTARTypes.h"
@@ -81,6 +80,3 @@ private:
     void updateInverseNonlinearJacobian(const mfem::Operator &grad) const;
     void updateInverseSchurCompliment() const;
 };
-
-
-#endif // POLY_UTILS_OPERATOR_H