[Task] Remove duplicate libxgboost requirement once upstream adds run_exports

Since, there is no run_exports for libxgboost yet, the libxgboost sits both in host and run.

This is a task to updated the recipe when xgboost supports run_exports

conda-forge/xgboost-feedstock#287

Start by reading the feedstock recipe and checking the upstream conda-forge/xgboost-feedstock#287 issue for run_exports support. Once upstream adds it, remove the duplicate libxgboost requirement from the host and run sections and verify the recipe keeps the dependency in the appropriate place.

Written by the indexing model from the issue text.