Remove [c] extras for sqlglot 30.x

[rolandwalker]

Description

sqlglot 30.x doesn't yet have a corresponding sqlglotc 30.x. This should keep us in a working and releasable state.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

I’m blocked from performing the review in this session because I can’t read the repo diff:

• Every local command fails with bwrap: loopback: Failed RTM_NEWADDR: Operation not permitted
• The web tool can’t access this PR/compare content directly

Please paste one of these, and I’ll do a focused review immediately:

1. git diff --stat 1051764c18613a3ace11c2f9278020c32089d9e2...97a3d4af7c78fad00eda427cb06d7b10c09cdb07
2. git diff 1051764c18613a3ace11c2f9278020c32089d9e2...97a3d4af7c78fad00eda427cb06d7b10c09cdb07
3. Or the PR “Files changed” patch text

Once shared, I’ll return concise findings limited to correctness, security, and missing tests/edge cases.

[rolandwalker]

There may have just been some kind of PyPi lag.