Disallow {index} being specified at the top level of _xpack/monitoring/_bulk

The general use case is to provide only the {type} to the bulk and even that may not be specified. However,
by setting it up as

/_x-pack/monitoring/{type}/_bulk
/_x-pack/monitoring/{index}/{type}/_bulk

it fails to properly recognize the {type} parameter because the PathTrie that gets generated sees two wildcards
at the same location and the last one specified wins -- {index}. As a result, it's impossible to only set the
{type} without making the PathTrie logic convoluted for a niche use case (a list to try instead of a single path).

his fixes the issue by removing the completely unused option: you can no longer specify {index} outside of
individual bulk indexing operations. If we see a need to bring it back, then we can add it as an API param, but
that is an unusual place for the index field and I do not expect it to be needed that frequently.

Original commit: elastic/x-pack-elasticsearch@40d0d05404

elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/rest/action/RestMonitoringBulkAction.java

@@ -38,8 +38,6 @@ public class RestMonitoringBulkAction extends MonitoringRestHandler {
         controller.registerHandler(PUT, URI_BASE + "/_bulk", this);
         controller.registerHandler(POST, URI_BASE + "/{type}/_bulk", this);
         controller.registerHandler(PUT, URI_BASE + "/{type}/_bulk", this);
-        controller.registerHandler(POST, URI_BASE + "/{index}/{type}/_bulk", this);
-        controller.registerHandler(PUT, URI_BASE + "/{index}/{type}/_bulk", this);
     }
 
     @Override

elasticsearch/x-pack/marvel/src/main/resources/monitoring-data.json

@@ -13,6 +13,9 @@
         "xpack.version": "${project.version}"
       }
     },
+    "kibana": {
+      "enabled": false
+    },
     "node": {
       "enabled": false
     }

elasticsearch/x-pack/marvel/src/test/resources/rest-api-spec/api/monitoring.bulk.json

@@ -4,12 +4,8 @@
     "methods": ["POST", "PUT"],
     "url": {
       "path": "/_x-pack/monitoring/_bulk",
-      "paths": ["/_x-pack/monitoring/_bulk", "/_x-pack/monitoring/{index}/_bulk", "/_x-pack/monitoring/{index}/{type}/_bulk"],
+      "paths": ["/_x-pack/monitoring/_bulk", "/_x-pack/monitoring/{type}/_bulk"],
       "parts": {
-        "index": {
-          "type" : "string",
-          "description" : "Default index for items which don't provide one"
-        },
         "type": {
           "type" : "string",
           "description" : "Default document type for items which don't provide one"