fix: remove __name__ matcher from processed matcher list

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Fix the bug reported by @dekelpilli in #1042 (comment)

The __name__ matcher is not removed after special preprocess logic, resulting in the afterword plan phase treating it as a column name.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

[killme2008]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (278e4c8) 85.79% compared to head (7dfb5a6) 85.34%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3213      +/-   ##
==========================================
- Coverage   85.79%   85.34%   -0.45%     
==========================================
  Files         840      840              
  Lines      137698   137698              
==========================================
- Hits       118136   117521     -615     
- Misses      19562    20177     +615