refactor: remove DXCC CW award and rename DXCC Mixed Mode to DXCC

- Removed dxcc-cw.json award definition
- Renamed "DXCC Mixed Mode" to "DXCC" in dxcc.json
- Changed award ID from "dxcc-mixed" to "dxcc"
- Removed dxcc-cw.json from awards service file list

Co-Authored-By: Claude <noreply@anthropic.com>

award-definitions/dxcc.json

@@ -1,6 +1,6 @@
 {
-  "id": "dxcc-mixed",
-  "name": "DXCC Mixed Mode",
+  "id": "dxcc",
+  "name": "DXCC",
   "description": "Confirm 100 DXCC entities on any band/mode",
   "caption": "Contact and confirm 100 different DXCC entities. Any band and mode combination counts. QSOs are confirmed when LoTW QSL is received.",
   "category": "dxcc",