Remove content type required setting

docs/reference/migration/migrate_8_0/http.asciidoc

@@ -8,6 +8,21 @@
 
 // end::notable-breaking-changes[]
 
+.The `http.content_type.required` setting has been removed.
+[%collapsible]
+====
+*Details* +
+The `http.content_type.required` setting was deprecated in Elasticsearch 6.0
+and has been removed in Elasticsearch 8.0. The setting was introduced in
+Elasticsearch 5.3 to prepare users for Elasticsearch 6.0, where content type
+auto detection was removed for HTTP requests.
+
+*Impact* +
+Discontinue use of the `http.content_type.required` system property.
+Specifying this property in `elasticsearch.yml` will result in an error on
+startup.
+====
+
 .The `http.tcp_no_delay` setting has been replaced by `http.tcp.no_delay`.
 [%collapsible]
 ====
@@ -35,4 +50,4 @@ Update your workflow and applications to assume `+` in a URL is encoded as
 `%2B`. Discontinue use of the `es.rest.url_plus_as_space` system property.
 Specifying this property in `elasticsearch.yml` will result in an error on
 startup.
-====
+====

qa/full-cluster-restart/build.gradle

@@ -35,7 +35,6 @@ for (Version bwcVersion : BuildParams.bwcVersions.indexCompatible) {
       numberOfNodes = 2
       // some tests rely on the translog not being flushed
       setting 'indices.memory.shard_inactive_time', '60m'
-      setting 'http.content_type.required', 'true'
       setting 'path.repo', "${buildDir}/cluster/shared/repo/${baseName}"
     }
   }

qa/rolling-upgrade/build.gradle

@@ -49,7 +49,6 @@ for (Version bwcVersion : BuildParams.bwcVersions.wireCompatible) {
 
       setting 'repositories.url.allowed_urls', 'http://snapshot.test*'
       setting 'path.repo', "${buildDir}/cluster/shared/repo/${baseName}"
-      setting 'http.content_type.required', 'true'
     }
   }
 

qa/verify-version-constants/build.gradle

@@ -32,7 +32,6 @@ for (Version bwcVersion : BuildParams.bwcVersions.indexCompatible) {
   testClusters {
     "${baseName}" {
       version = bwcVersion.toString()
-      setting 'http.content_type.required', 'true'
     }
   }
 

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -264,7 +264,6 @@ public void apply(Settings value, Settings current, Settings previous) {
             HttpTransportSettings.SETTING_CORS_ALLOW_METHODS,
             HttpTransportSettings.SETTING_CORS_ALLOW_HEADERS,
             HttpTransportSettings.SETTING_HTTP_DETAILED_ERRORS_ENABLED,
-            HttpTransportSettings.SETTING_HTTP_CONTENT_TYPE_REQUIRED,
             HttpTransportSettings.SETTING_HTTP_MAX_CONTENT_LENGTH,
             HttpTransportSettings.SETTING_HTTP_MAX_CHUNK_SIZE,
             HttpTransportSettings.SETTING_HTTP_MAX_HEADER_SIZE,

server/src/main/java/org/elasticsearch/http/HttpTransportSettings.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.http;
 
-import org.elasticsearch.common.Booleans;
 import org.elasticsearch.common.network.NetworkService;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Setting.Property;
@@ -72,15 +71,6 @@ public final class HttpTransportSettings {
         intSetting("http.publish_port", -1, -1, Property.NodeScope);
     public static final Setting<Boolean> SETTING_HTTP_DETAILED_ERRORS_ENABLED =
         Setting.boolSetting("http.detailed_errors.enabled", true, Property.NodeScope);
-    public static final Setting<Boolean> SETTING_HTTP_CONTENT_TYPE_REQUIRED =
-        new Setting<>("http.content_type.required", (s) -> Boolean.toString(true), (s) -> {
-            final boolean value = Booleans.parseBoolean(s);
-            if (value == false) {
-                throw new IllegalArgumentException("http.content_type.required cannot be set to false. It exists only to make a rolling" +
-                    " upgrade easier");
-            }
-            return true;
-        }, Property.NodeScope, Property.Deprecated);
     public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_CONTENT_LENGTH =
         Setting.byteSizeSetting(
                 "http.max_content_length",

x-pack/qa/rolling-upgrade/build.gradle

@@ -42,7 +42,6 @@ for (Version bwcVersion : BuildParams.bwcVersions.wireCompatible) {
 
       setting 'repositories.url.allowed_urls', 'http://snapshot.test*'
       setting 'path.repo', "${buildDir}/cluster/shared/repo/${baseName}"
-      setting 'http.content_type.required', 'true'
       setting 'xpack.license.self_generated.type', 'trial'
       setting 'xpack.security.enabled', 'true'
       setting 'xpack.security.transport.ssl.enabled', 'true'