[Rust] [DataFusion] Remove use of threads and channels from ParquetScanExec

[asfimport]

At the time I implemented the parquet scan exec I thought it was necessary to run in a thread and use channels to communicate but this can be avoided in conjunction with other changes in the parent issue.

Reporter: Andy Grove / @andygrove
Assignee: Andy Grove / @andygrove

_{Note: This issue was originally created as ARROW-9708. Please see the migration documentation for further details.}