Revert "OpenSSL::KDF.scrypt needs EVP_PBE_scrypt()"

This reverts commit d434765fae.

spec/ruby/library/openssl/kdf/scrypt_spec.rb

@@ -2,8 +2,6 @@ require_relative '../../../spec_helper'
 require 'openssl'
 
 describe "OpenSSL::KDF.scrypt" do
-  break unless defined?(OpenSSL::KDF.scrypt)
-
   before :each do
     @defaults = {
       salt: "\x00".b * 16,