Remove old comment

This comment is not valid since that `if` is there to make possible to
do:

    remove_index :users, :name

Instead of:

    remove_index :users, column: :name

What is a valid use case.

[ci skip]

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -422,7 +422,7 @@ def rename_index(table_name, old_name, new_name)
       end
 
       def index_name(table_name, options) #:nodoc:
-        if Hash === options # legacy support
+        if Hash === options
           if options[:column]
             "index_#{table_name}_on_#{Array(options[:column]) * '_and_'}"
           elsif options[:name]