[REMOVAL] Removed deprecated semantic convention header files.

[marcalff]

Fixes #3169

Removed deprecated code, as announced earlier on Nov 9, 2024:

Deprecation is announced as part of the migration to weaver:

* `Version:` release following opentelemetry-cpp 1.17.0
* `Date:` Nov 9, 2024
* `PR:` [PR 3105](https://github.com/open-telemetry/opentelemetry-cpp/pull/3105)

Changes

Please provide a brief description of the changes here.

• Removed deprecated semantic convention headers.
• Updated maintainers documentation to reflect the new process with weaver.

For significant contributions please make sure you have completed the following items:

• [ ] CHANGELOG.md updated for non-trivial changes
• [ ] Unit tests have been added
• [ ] Changes in public API reviewed

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.92%. Comparing base (3d901a8) to head (d569ad4). Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3475      +/-   ##
==========================================
+ Coverage   89.91%   89.92%   +0.02%     
==========================================
  Files         219      219              
  Lines        7042     7042              
==========================================
+ Hits         6331     6332       +1     
+ Misses        711      710       -1     

see 1 file with indirect coverage changes

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[marcalff]

LGTM. Although it was deprecated, it's still worth including a changelog entry with migration steps for those who haven't removed it yet.

Good idea, thanks. Implemented, waiting for CI to complete.