Remove fmt version requirement

[pierrepebay]

• We test vt with fmt 11.1.3 (see Cuda 11.4.3-devel-ubuntu20.04 image in workflows repository for details)
• fmt 7.1.3 doesn't align with distBVH needs: #37: Use master branch of darma spack package sandialabs/distBVH#42 (review).

The best way forward might be removing fmt version requirement (we don't explicitly provide it in vt anyways).