Un-deprecate DataFrame.from_items()
Under #18262 a `FutureWarning` was added suggesting that existing code like this:

    pd.DataFrame.from_items(x)

Should be changed to this:

    import collections
    pd.DataFrame.from_dict(collections.OrderedDict(x))

The fact that `from_items()` appeared only 6 times (now 8 times) in a Stack Overflow search was used as partial justification for removing it.  But if you search on GitHub, [`pd.DataFrame.from_items()`](https://github.com/search?q=pd.DataFrame.from_items&type=Code) appears more than 15,000 times in Python--almost half as many as `from_records()`!

We should celebrate the fact that this function doesn't cause enough confusion to appear often on Stack Overflow.  But it does occur (a lot!) in real code, and deprecating it is a mistake.

If constructing a temporary `OrderedDict` around items is the best way to construct a DataFrame, Pandas should implement that as a short function called `DataFrame.from_items()`, rather than asking thousands of people to busy themselves to accommodate this unnecessary API change.

I recommend removing the FutureWarning, and retaining this widely-used, longstanding function.

For reference, the `FutureWarning` starts in 0.23 and looks like this:

> FutureWarning: from_items is deprecated. Please use DataFrame.from_dict(dict(items), ...) instead. DataFrame.from_dict(OrderedDict(items)) may be used to preserve the key order.

