As described in Automatic linking of MFC library versions "The MFC header files automatically determine the correct version of the MFC library to link, based on values defined in your build environment. The MFC header files add compiler directives instructing the linker to link in a specific version of the MFC library."
If the C++ project file (.vcxproj) generated when an old VS2008 MFC project was converted contains references to the old MFC libraries in the linker property pages you can remove them. You can also review your source code for any #pragma directives that refer to the old libraries.