[wpilibc] Move NullDeleter from frc/Base.h to wpi/NullDeleter.h (#3387)

frc/Base.h was also deleted because it's now empty.

wpiutil/src/main/native/include/wpi/NullDeleter.h

@@ -0,0 +1,16 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+namespace wpi {
+
+// A struct to use as a deleter when a std::shared_ptr must wrap a raw pointer
+// that is being deleted by someone else.
+template <class T>
+struct NullDeleter {
+  void operator()(T*) const noexcept {};
+};
+
+}  // namespace wpi