Unify WordPress migration content

[stevector]

Expected behavior

When I google for "Pantheon WordPress migration" I get one reliable entry point as the top result. And lower results fit into a coherent flow of information.

Actual behavior

Old and duplicative results come up first:

• https://pantheon.io/resources/quickstart-guide-migrating-wordpress-site
• https://docs.pantheon.io/migrate-wordpress

Steps to reproduce the problem

1. https://www.google.com/search?q=pantheon+wordpress+migration

Suggested Resolution

• Remove old stuff and redirect to https://pantheon.jp/docs/guides/wordpress-pantheon/migrate-existing-wp-site
• These page should probably be also folded into the general guide:
  • https://pantheon.jp/docs/guides/wpengine/migrate
  • https://pantheon.jp/docs/migrate-manual
  • https://pantheon.jp/docs/guides/guided

Additional information

My suggestion is probably overly simplistic and risks SEO benefits of old content. Please discuss with RJ Horning for a general redirect/SEO perspective. Also, please discuss with @scottbuscemi