Remove dead code identified by deadcode tool (#37271)

Ran [`deadcode`](https://pkg.go.dev/golang.org/x/tools/cmd/deadcode)
(`-test ./...`) to find functions, methods and error types unreachable
from any call path (including tests), and removed the truly-dead ones.

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

services/context/user.go

@@ -30,27 +30,6 @@ func UserAssignmentWeb() func(ctx *Context) {
 	}
 }
 
-// UserIDAssignmentAPI returns a middleware to handle context-user assignment for api routes
-func UserIDAssignmentAPI() func(ctx *APIContext) {
-	return func(ctx *APIContext) {
-		userID := ctx.PathParamInt64("user-id")
-
-		if ctx.IsSigned && ctx.Doer.ID == userID {
-			ctx.ContextUser = ctx.Doer
-		} else {
-			var err error
-			ctx.ContextUser, err = user_model.GetUserByID(ctx, userID)
-			if err != nil {
-				if user_model.IsErrUserNotExist(err) {
-					ctx.APIError(http.StatusNotFound, err)
-				} else {
-					ctx.APIErrorInternal(err)
-				}
-			}
-		}
-	}
-}
-
 // UserAssignmentAPI returns a middleware to handle context-user assignment for api routes
 func UserAssignmentAPI() func(ctx *APIContext) {
 	return func(ctx *APIContext) {