vision: delete obsolete beta snippets for logo detection (#3114)

v1 snippets are published, via #3098 and shown on this docs page: https://cloud.google.com/video-intelligence/docs/logo-recognition

So we're deleting the beta snippets which are now obsolete. 

[Set up pre-launch as _draft_, will push this change through once the above PR is complete and the docs are updated]

Author: czahedi