Remove unused `parquet::format` crate

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

• part of [EPIC] A collection of items to improve speed of parquet metadata encoding #5853

The parquet::format module contains auto generated code for parsing data in the parquet.thrift format

After we merge #8530 from @etseidl these structures will no longer be needed and their presence is ust confusing

I tested it out a bit locally and the only place the thrift structures are now used is in the parquet-format tool and some benchmarks

Describe the solution you'd like
Delete the parquet::format module (parquet/src/format.rs), and update the tools to use the new thrift structures

Describe alternatives you've considered

Additional context

[etseidl]

Thanks to @lichuang we're halfway to completing this.

A question that came up is do we want to keep parquet-layout. There are other tools that display page information in more detail. If we want to keep it, then we'll need to add something to the metadata reader to extract page header info. Or we could try to leverage the page encoding stats and offset index if they're available.

[etseidl]

I also wonder if we should deprecate format before removing it.