Test: Remove broken yml test feature (elastic#31255)

The `requires_replica` yaml test feature hasn't worked for years. This
is what happens if you try to use it:
```
   > Throwable #1: java.lang.NullPointerException
   >    at __randomizedtesting.SeedInfo.seed([E6602FB306244B12:6E341069A8D826EA]:0)
   >    at org.elasticsearch.test.rest.yaml.Features.areAllSupported(Features.java:58)
   >    at org.elasticsearch.test.rest.yaml.section.SkipSection.skip(SkipSection.java:144)
   >    at org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase.test(ESClientYamlSuiteTestCase.java:321)
```

None of our tests use it.

Author: nik9000

test/framework/src/main/java/org/elasticsearch/test/rest/yaml/Features.java

@@ -19,8 +19,6 @@
 
 package org.elasticsearch.test.rest.yaml;
 
-import org.elasticsearch.test.ESIntegTestCase;
-
 import java.util.Arrays;
 import java.util.List;
 
@@ -54,9 +52,6 @@ private Features() {
      */
     public static boolean areAllSupported(List<String> features) {
         for (String feature : features) {
-            if ("requires_replica".equals(feature) && ESIntegTestCase.cluster().numDataNodes() >= 2) {
-                continue;
-            }
             if (!SUPPORTED.contains(feature)) {
                 return false;
             }