Align RestTemplateBuilder with Framework's removal of OkHttp 2 support

Closes gh-13314

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/client/RestTemplateBuilder.java

@@ -72,8 +72,6 @@ public class RestTemplateBuilder {
 				"org.springframework.http.client.HttpComponentsClientHttpRequestFactory");
 		candidates.put("okhttp3.OkHttpClient",
 				"org.springframework.http.client.OkHttp3ClientHttpRequestFactory");
-		candidates.put("com.squareup.okhttp.OkHttpClient",
-				"org.springframework.http.client.OkHttpClientHttpRequestFactory");
 		REQUEST_FACTORY_CANDIDATES = Collections.unmodifiableMap(candidates);
 	}