Remove arena crate dependency

[xrl]

The src/lib.rs has a extern crate arena line. Where is that used? I looked for use of the arena crate and I didn't find anything.

If I remove it, the parquet-read/parquet-schema binary executables don't need any dylib paths.

With arena:

$ cargo install --force
$ ~/.cargo/bin/parquet-schema 
dyld: Library not loaded: @rpath/libarena-9fcb98fa681bdaef.dylib
  Referenced from: /Users/xavierlange/.cargo/bin/parquet-schema
  Reason: image not found
Abort trap: 6

Without arena:

$ cargo install --force
$ ~/.cargo/bin/parquet-schema 
Usage: parquet-schema <file-path> [verbose]

Are we open to removing the extern crate arena line from src/lib.rs?

[sunchao]

Good point. We don't need the line. It is already removed in the arrow project though.

[xrl]

Cool, closing!