fix(auth): drop unreachable redirect_uris guard for coverage

Pydantic already requires redirect_uris with min_length=1; the handler
check was unreachable and blocked 100% coverage.

Author: KirtiRamchandani

src/mcp/server/auth/handlers/register.py

@@ -91,15 +91,6 @@ async def handle(self, request: Request) -> Response:
                 status_code=400,
             )
 
-        if not client_metadata.redirect_uris:
-            return PydanticJSONResponse(
-                content=RegistrationErrorResponse(
-                    error="invalid_client_metadata",
-                    error_description="redirect_uris is required",
-                ),
-                status_code=400,
-            )
-
         for redirect_uri in client_metadata.redirect_uris:
             try:
                 validate_registered_redirect_uri(redirect_uri)