Draft: Remove ff table existence check in Multistore

What does this MR do and why?

Describe in detail what your merge request does and why.

Screenshots or screen recordings

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How to set up and validate locally

➜  RAILS_ENV=test bundle exec rake db:purge
➜  gdk psql
psql (12.13)
Type "help" for help.

gitlabhq_development=# \c gitlabhq_test
You are now connected to database "gitlabhq_test" as user "sylvesterchin".
gitlabhq_test=# \dt
Did not find any relations.

➜  RAILS_ENV=test bundle exec rake db:setup
Database 'gitlabhq_test' already exists
Database 'gitlabhq_test_ci' already exists

Both purge and setup runs on this branch.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.