Remove work-around for "non-existent include directory" problem in Smith installs

[chapman39]

For downstream Smith users, we have this work-around to remove non-existent paths to interface include directories. It would be nice to get to the bottom of the issue and remove the necessity for the work-around, which can be seen here: https://github.com/llnl/smith/blob/develop/examples/using-with-cmake/CMakeLists.txt#L18-L52

I think it may be possible to remove the directory within Smith itself, so that once it comes to a user who wants to link with smith::smith, they don't have to worry about it.

I think it has to do with MFEM setting invalid include paths to netlib-scalapack and perhaps others, so maybe this should be fixed in MFEM itself.

abbreviated warning:

-- Configuring done
CMake Error in <path>/CMakeLists.txt:
  Imported target "<target>" includes non-existent path

    "<path>/llvm-19.1.3/netlib-scalapack-2.2.2-tixdyfasces7aid2hzhwrxbw2xafy2ie/include"

  in its INTERFACE_INCLUDE_DIRECTORIES.  Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.



-- Generating done
CMake Generate step failed.  Build files cannot be regenerated correctly.