Move ECP TLS 1.3 handling back to TLS layer

[lhuang04]

Summary: PR 343 refactor introduced some discrepancy in crypto library between tls13-prototype and development branch. However there seems no plan to upstream it back to development branch.

Move the ECP TLS 1.3 handling back to TLS layer. This can remove the crypto library difference between tls13-prototype branch and development branch.

Test Plan:

ssl-opt.sh -p -s -f "TLS 1.3: "

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  Description

  A few sentences describing the overall goals of the pull request's commits.

Status

READY/IN DEVELOPMENT/HOLD

Requires Backporting

When there is a bug fix, it should be backported to all maintained and supported branches. Changes do not have to be backported if:

• This PR is a new feature\enhancement
• This PR contains changes in the API. If this is true, and there is a need for the fix to be backported, the fix should be handled differently in the legacy branch

Yes | NO
Which branch?

Migrations

If there is any API change, what's the incentive and logic for it.

YES | NO

Additional comments

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Todos

• [ ] Tests
• [ ] Documentation
• [ ] Changelog updated
• [ ] Backported

Steps to test or reproduce

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[lhuang04]

This may no longer be needed. There seems to be no libcrypto difference between development and tls13-prototype. The one left over, ecp_internal.h was also no longer in the latest development branch.