[Rust] Remove OffsetSize::prefix

[asfimport]

Background:
Left over cleanups suggested by from @sunchao on #9425

Broken out from #9508

Rationale:
This function is redundant with OffsetSize::is_large

Reporter: Andrew Lamb / @alamb
Assignee: Andrew Lamb / @alamb

PRs and other links:

• GitHub Pull Request #9690

_{Note: This issue was originally created as ARROW-11951. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Issue resolved by pull request 9690
#9690