[ci skip] Update Performance Testing guide.

[siong1987]

• remove Palmist which is no longer available.
• update link to Query Reviewer.

[vijaydev]

@siong1987 please note that you can do such changes in docrails directly instead of sending in pull requests. Thanks.

[siong1987]

@vijaydev got it. it is a bit confusing on the roles of both docrails and rails master. but, got it now. thanks.

[frodsan]

@siong1987 you can check Contributing to Rails Documentation guide.

"If you're confident about your changes, you can push them directly yourself via docrails. Docrails is a branch with an open commit policy and public write access. Commits to docrails are still reviewed, but this happens after they are pushed. Docrails is merged with master regularly, so you are effectively editing the Ruby on Rails documentation."