[librtmp] Update to 2024-03-01

[paperchalice]

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download.
• The "supports" clause reflects platforms that may be fixed by this new version.
• Any fixed CI baseline entries are removed from that file.
• Any patches that are no longer applied are deleted from the port's directory. OpenSSL issues are fixed by upstream.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is added to each modified port's versions file.

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• Use the latest commit (2.6).
• Provide pkgconfig file, so curl can consume it. (May open another PR to add it.)
• Rename target librtmp to rtmp so pkg-config can work correctly.
• Use vcpkg zlib in librtmp.pc.