Remove deprecated $with_column() and subnamespace $arr

[etiennebacher]

@sorhawell apparently Expr_list is defined twice and the first definition is a deprecated function (no idea since when it's deprecated):

r-polars/R/expr__expr.R

Lines 4224 to 4230 in 33a56d9

	Expr_list = function() {
	if (is.null(runtime_state$warned_deprecate_list)) {
	runtime_state$warned_deprecate_list = TRUE
	warning("polars pl$list and <Expr>$list are deprecated, use $implode instead.")
	}
	self$implode()
	}

Do you want to remove this now?

[sorhawell]

oh yes the expression <Expr>$list was deprecated/renamed in py-polars to <Expr>$implode() we followed suit already in r-polars 0.6.0 4 months ago

We accidentially hard removed it from 0.8.1 when renaming arr to list but that was about to some no harm is done.

We can delete Expr_list, yes.

[sorhawell]

Looks good to me :)