Update HOGP tutorial to use fit_gpytorch_mll_torch & _fast_solves (#1686)

Summary:
Pull Request resolved: #1686

This now runs ~25% faster on my devserver.

Reviewed By: esantorella

Differential Revision: D43374145

fbshipit-source-id: 8df246a83029fb4880b3f73099615c0549c85e6d

Author: saitcakmak

scripts/run_tutorials.py

@@ -38,7 +38,6 @@
     "thompson_sampling.ipynb",  # very slow without KeOps + GPU
     "composite_mtbo.ipynb",  # TODO: very slow, figure out if we can make it faster
     "Multi_objective_multi_fidelity_BO.ipynb",  # TODO: very slow, speed up
-    "composite_bo_with_hogp.ipynb",  # TODO: OOMing the nightly cron, reduce mem usage
 }