Cleanup regex_expressions.rs to remove _regexp_match function

[Omega359]

Which issue does this PR close?

Closes #9106

Rationale for this change

Code cleanup.

What changes are included in this PR?

Code removal, minor code cleanup, toml file updates.

Are these changes tested?

Yes

Are there any user-facing changes?

No.

[alamb]

Thanks @Omega359 -- the code looks great. I am running some benchmarks just to be sure

[alamb]

@viirya fixed the problem in #8631

I ran some of the queries from that PR:

❯ SELECT COUNT(*) FROM 'index' WHERE
    ARRAY_LENGTH(
      REGEXP_MATCH(path, '\\.(asm|c|cc|cpp|cxx|h|hpp|rs|[Ff][0-9]{0,2}(?:or)?|go)$')
    ) > 0;

on 7.2 GB of parquet data

$ du -s -h index
7.2G	index

Main (without this PR):

1 row in set. Query took 4.820 seconds.

This PR:

1 row in set. Query took 4.760 seconds.

So basically the same.

Thank you @Omega359 -- very nice cleanup 🧹

[alamb]

Thank you @Omega359 and @viirya 🚀