Refactor `PostgreSQL::TableDefinition#primary_key`

Because call the `column` method and set the `options[:primary_key]` is
handled at `super`, here need only treat the `options[:default]`.

activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb

@@ -125,10 +125,8 @@ class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, options = {})
-          return super unless type == :uuid
-          options[:default] = options.fetch(:default, 'uuid_generate_v4()')
-          options[:primary_key] = true
-          column name, type, options
+          options[:default] = options.fetch(:default, 'uuid_generate_v4()') if type == :uuid
+          super
         end
 
         def new_column_definition(name, type, options) # :nodoc: