chore(parquet): remove deprecated schema-coercion helpers (Closes #23080 - partial)

[Dodothereal]

Removes coerce_file_schema_to_view_type and coerce_file_schema_to_string_type (both deprecated since 47.0.0 with replacement apply_file_schema_type_coercions). Zero callers in the workspace; only the function definitions and re-export entries in mod.rs / file_format.rs remain. Drops the now-unused #[expect(deprecated)] attribute on the re-export lines. Pure 118-line deletion across 3 files. Part of #23080 (partial - third in the housekeeping series after #23129 and #23131). AI assistance: used an AI coding assistant to identify and remove unused symbols; verified via repo-wide grep that the deprecated functions have no callers.

[alamb]

Thank you (again) @Dodothereal

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
    Building datafusion-datasource-parquet v54.0.0 (current)
       Built [  49.335s] (current)
     Parsing datafusion-datasource-parquet v54.0.0 (current)
      Parsed [   0.030s] (current)
    Building datafusion-datasource-parquet v54.0.0 (baseline)
       Built [  43.008s] (baseline)
     Parsing datafusion-datasource-parquet v54.0.0 (baseline)
      Parsed [   0.030s] (baseline)
    Checking datafusion-datasource-parquet v54.0.0 -> v54.0.0 (no change; assume patch)
     Checked [   0.151s] 223 checks: 222 pass, 1 fail, 0 warn, 30 skip

--- failure function_missing: pub fn removed or renamed ---

Description:
A publicly-visible function cannot be imported by its prior path. A `pub use` may have been removed, or the function itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.48.0/src/lints/function_missing.ron

Failed in:
  function datafusion_datasource_parquet::file_format::coerce_file_schema_to_view_type, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/3dc49bbe5c0d3aa54f08abe1d8e964ca9507b586/datafusion/datasource-parquet/src/schema_coercion.rs:426
  function datafusion_datasource_parquet::coerce_file_schema_to_view_type, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/3dc49bbe5c0d3aa54f08abe1d8e964ca9507b586/datafusion/datasource-parquet/src/schema_coercion.rs:426
  function datafusion_datasource_parquet::file_format::coerce_file_schema_to_string_type, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/3dc49bbe5c0d3aa54f08abe1d8e964ca9507b586/datafusion/datasource-parquet/src/schema_coercion.rs:479
  function datafusion_datasource_parquet::coerce_file_schema_to_string_type, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/3dc49bbe5c0d3aa54f08abe1d8e964ca9507b586/datafusion/datasource-parquet/src/schema_coercion.rs:479

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [  93.744s] datafusion-datasource-parquet

[alamb]

I took the liberty of merging up from main and fixing the clippy error and pushing to your branch