GFR: Fix extent data or delete field

[jmfcoleman]

The extent field seems to be off for many series. For example, for the Committee on Accounts (RG 233), the series of committee papers shows the extent as undefined. But when you click on the link to the committee papers series, it shows 8 linear feet and 7 linear inches of records. And under RG 148, the entry for the Antitrust Modernization Commission lists only 11 data files with 3 linear inches of documentation, but the Catalog record states that there are 12 linear feet of textual records. If this field cannot be reliably populated, perhaps it should be deleted.