Removed non-sdk best practice documentation

[austinvalle]

closes #1151

Related PRs:

• Added redirects for SDKv2 best practices migration to Plugin Framework terraform-website#2474
• Added new Plugin Development best practices section (migrated from SDKv2 repo) terraform-docs-common#295
• Add deprecation documentation (from Best Practices - SDKv2) terraform-plugin-framework#684

Notes

• Should I add a callout on Overview page of SDKv2 that some sections have been moved to the Plugin Development section? - https://developer.hashicorp.com/terraform/plugin
• I left the deprecation notes and drift documentation as the framework got it's own version (see PRs above) and these seem to still be relevant.
• The testing patterns page was already migrated: hashicorp/terraform-plugin-testing@5642b4f#diff-a573c95058afb41d13b5d4429a0438baaf4660189ae84ddea617154200e5b84d. I added a redirect for this in the terraform-website PR
• Fixed wording in deprecation docs that refer to attributes when it should be resources
• Updated links that will be available after merging terraform-docs-common PR

[bendbennett]

LGTM 👍

As you suggested, a callout on Overview page of SDKv2 that some sections have been moved to the Plugin Development section sounds like a good idea.

[austinvalle]

As you suggested, a callout on Overview page of SDKv2 that some sections have been moved to the Plugin Development section sounds like a good idea.

Added in aa8be73

[bflad]

Looks good to me 🚀

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