Remove ServerWebExchange::getParts and ServerRequest::parts

Revert to state before DefaultMultipartMessageReader

spring-test/src/main/java/org/springframework/mock/web/reactive/function/server/MockServerRequest.java

@@ -249,13 +249,6 @@ public final class MockServerRequest implements ServerRequest {
 		return (Mono<MultiValueMap<String, Part>>) this.body;
 	}
 
-	@Override
-	@SuppressWarnings("unchecked")
-	public Flux<Part> parts() {
-		Assert.state(this.body != null, "No body");
-		return (Flux<Part>) this.body;
-	}
-
 	@Override
 	public ServerWebExchange exchange() {
 		Assert.state(this.exchange != null, "No exchange");