feat!: remove v1 headers behavior

[markdalgleish]

This PR removes the v2_headers flag, making it the new default behavior.

[changeset-bot]

🦋 Changeset detected

Latest commit: f1379c0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@remix-run/dev	Major
@remix-run/react	Major
@remix-run/server-runtime	Major
@remix-run/testing	Major
@remix-run/cloudflare	Major
@remix-run/deno	Major
@remix-run/node	Major
@remix-run/cloudflare-pages	Major
@remix-run/cloudflare-workers	Major
@remix-run/architect	Major
@remix-run/express	Major
@remix-run/netlify	Major
@remix-run/serve	Major
@remix-run/vercel	Major
create-remix	Major
remix	Major
@remix-run/css-bundle	Major
@remix-run/eslint-config	Major

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[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-b3de370-20230731 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

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[github-actions]

🤖 Hello there,

We just published version 1.19.2-pre.1 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-7cb1e7e-20230803 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

We just published version 1.19.2-pre.2 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-6e250f7-20230805 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-a179aa7-20230809 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-b1149bb-20230810 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!