[C++] Remove IR Consumer

[asfimport]

At one point there were two ongoing proposals for serializing exec plans. An Arrow proposal (ir_consumer) and Substrait. In general it is perfectly ok to have multiple representations of the exec plan. So if someone wants the ir_consumer for whatever reason we can keep ti. However, I believe the ir_consumer representation is no longer being actively maintained / expanded and so we should probably remove it to avoid confusion.

Reporter: Weston Pace / @westonpace
Assignee: Weston Pace / @westonpace

Related issues:

• [Docs] Remove page for "Compute IR" (is related to)

PRs and other links:

• GitHub Pull Request #13301

_{Note: This issue was originally created as ARROW-16740. Please see the migration documentation for further details.}

[asfimport]

Weston Pace / @westonpace:
Issue resolved by pull request 13301
#13301