ARROW-12614: [C++][Compute] Remove support for Tables in ExecuteScalarExpression

[bkietz]

Cleanup PR after ARROW-11929 which added untested support for ExecuteScalarExpression(Table).

[github-actions]

https://issues.apache.org/jira/browse/ARROW-12614

[nealrichardson]

I started deleting some R code in #10191 by using InMemoryDataset; can we discuss tradeoffs of the two approaches?

[lidavidm]

LGTM, though there's one MSVC error to be fixed.

Regardless of whether we go a different direction, we'll probably want this since the current code path simply bails unexpectedly/crashes.

[bkietz]

The InMemoryDataset approach is more aligned with dplyr, so if that's straightforward and sufficient then I'd say we probably don't want this (and I'll delete the Datum::TABLE) path. If there's interest in replacing simpler vector expressions with calls to ExecuteScalarExpression, then this might be still be useful for things like Array$create(c(1,2,3)) + Array$create(c(1,4,5))

[lidavidm]

The AppVeyor build is still failing due to a syntax error, oddly.