Back out "Add example of LLava encoder" (#2420)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2420

It breaks CI since LLava is not installed into the repo yet. Loading a full LLava model may put load in the CI. Reverting it till a better solution is found.

Original commit changeset: 57f79a925f40

Original Phabricator Diff: D54812717

bypass-github-export-checks

Reviewed By: Gasoonjia, cccclai

Differential Revision: D54880586

fbshipit-source-id: 5b3667d0ef6c86bc52361b32101a99a9157dd750