foreigner – remove foreign key

# Removes the given foreign key from the table.
# Removes the foreign key on +accounts.branch_id+.
remove_foreign_key :accounts, :branches

# Removes the foreign key on +accounts.owner_id+.
remove_foreign_key :accounts, column: :owner_id

# Removes the foreign key named +special_fk_name+ on the +accounts+ table.
remove_foreign_key :accounts, name: :special_fk_name

Offical doc: http://api.rubyonrails.org/v4.2/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-remove_foreign_key