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

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 /CMakeLists.txt:
Imported target "" includes non-existent 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.
```