docs: remove Appendix C (unsigned types don't exist in 2.0)

Author: claude

docs/design/multi-backend-plan.md

@@ -666,13 +666,4 @@ date, time, timetz, timestamp, timestamptz, interval
 uuid
 json, jsonb
 array types (e.g., integer[])
-```
-
-## Appendix C: Removed from Core Types
-
-| Type | Reason | Alternative |
-|------|--------|-------------|
-| `uint8` | No PostgreSQL equivalent | Use `int16` or MySQL native `tinyint unsigned` |
-| `uint16` | No PostgreSQL equivalent | Use `int32` or MySQL native `smallint unsigned` |
-| `uint32` | No PostgreSQL equivalent | Use `int64` or MySQL native `int unsigned` |
-| `uint64` | No PostgreSQL equivalent | Use `int64` (if range fits) or MySQL native `bigint unsigned` |
+```