unsetting a few more variables that arent needed outside of this function

src/citra_qt/CMakeLists.txt

@@ -106,4 +106,7 @@ if (Qt5_FOUND AND MSVC)
     )
     unset(Qt5_DLLS)
     unset(Qt5_DLL_DIR)
+    unset(Qt5_PLATFORMS_DIR)
+    unset(DLL_DEST)
+    unset(PLATFORMS)
 endif()