Reorganize some of the Diameter XML files, taking advantage of the fact that

Reorganize some of the Diameter XML files, taking advantage of the fact that
AVPs can be grouped by Vendor now (not just by Application).

Move a bunch of vendor-specific Application IDs to the vendor's XML file.

Delete the (basically empty) SKT.xml, ChinaTelecom.xml, and VerizonWireless.xml
files.

Fix a typo: 16777224 is 3GPP Gx, not 3GPP Cx.

Use (derived) type Enumerated (rather than Unsigned32 or Integer32) when the
AVP is of type Enumerated.

Change-Id: I7a9702c0c48dc3fe751ad74413d8ecc040984f1f
Reviewed-on: https://code.wireshark.org/review/8235
Petri-Dish: Jeff Morriss <jeff.morriss.ws@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>