on new tenant model creation migrate private schemas rather than load from the schema.rb

This solves the problem where the private schema schema_versions table does not contain the complete set of migration versions after creating a new tenant model
remove problematic code that was incorrectly pruning public schema versions
Merge pull request #9 from felafelwaffle/felafelwaffle-fix-new-tenant-missing-migrations

fix missing private schema migrations when creating a new tenant model