Fix English language infinite loop between TRUNCATE and DELETE pages

[rmloveland]

On the TRUNCATE page we say (roughly) that

It's faster to delete smaller tables using a DELETE without a WHERE clause than to use TRUNCATE

But we don't say what smaller is!

Then, on the DELETE page we say that

The TRUNCATE statement removes all rows from a table by dropping the table and recreating a new table ... this is much more performant than deleting rows ...

Scope of work here is roughly:

1. Clarify what is meant by "smaller", and thus when to prefer DELETE minus WHERE vs TRUNCATE
2. Update language to break the "infinite loop" between these pages' instructions :-)
3. Othher work as needed to achieve the above