[wpigui] Remove wpiutil linkage (#3851)

It was only being used for fs::remove() (added in #3463), which is easily
replaced by std::remove().

The code change does not affect the WPILib tools, as this code is not used when JSON save files are used.

wpigui/src/main/native/cpp/wpigui.cpp

@@ -15,7 +15,6 @@
 #include <imgui_internal.h>
 #include <implot.h>
 #include <stb_image.h>
-#include <wpi/fs.h>
 
 #include "wpigui_internal.h"
 
@@ -320,7 +319,7 @@ void gui::Main() {
 
   // Delete the save file if requested.
   if (!gContext->saveSettings && gContext->resetOnExit) {
-    fs::remove(fs::path{gContext->iniPath});
+    std::remove(gContext->iniPath.c_str());
   }
 
   glfwDestroyWindow(gContext->window);