Elasticsearch: Remove support for EOL 6.6 version

As that version is now EOL as of July 29, 2020 ([1]).

Update the config-gerrit documentation accordingly, by linking to the
current Elasticsearch documentation now.

[1] https://www.elastic.co/support/eol

Change-Id: Ied980886440869cc5cdbfc1dd915c0375a2f36e1
diff --git a/java/com/google/gerrit/elasticsearch/ElasticVersion.java b/java/com/google/gerrit/elasticsearch/ElasticVersion.java
index 62fcfda..c79a25e 100644
--- a/java/com/google/gerrit/elasticsearch/ElasticVersion.java
+++ b/java/com/google/gerrit/elasticsearch/ElasticVersion.java
@@ -18,7 +18,6 @@
 import java.util.regex.Pattern;
 
 public enum ElasticVersion {
-  V6_6("6.6.*"),
   V6_7("6.7.*"),
   V6_8("6.8.*"),
   V7_0("7.0.*"),
diff --git a/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java b/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
index a51cda4..60bf64c 100644
--- a/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
+++ b/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
@@ -38,8 +38,6 @@
 
   private static String getImageName(ElasticVersion version) {
     switch (version) {
-      case V6_6:
-        return "blacktop/elasticsearch:6.6.2";
       case V6_7:
         return "blacktop/elasticsearch:6.7.2";
       case V6_8:
diff --git a/javatests/com/google/gerrit/elasticsearch/ElasticVersionTest.java b/javatests/com/google/gerrit/elasticsearch/ElasticVersionTest.java
index 7e43732..6295672 100644
--- a/javatests/com/google/gerrit/elasticsearch/ElasticVersionTest.java
+++ b/javatests/com/google/gerrit/elasticsearch/ElasticVersionTest.java
@@ -22,9 +22,6 @@
 public class ElasticVersionTest extends GerritBaseTests {
   @Test
   public void supportedVersion() throws Exception {
-    assertThat(ElasticVersion.forVersion("6.6.0")).isEqualTo(ElasticVersion.V6_6);
-    assertThat(ElasticVersion.forVersion("6.6.1")).isEqualTo(ElasticVersion.V6_6);
-
     assertThat(ElasticVersion.forVersion("6.7.0")).isEqualTo(ElasticVersion.V6_7);
     assertThat(ElasticVersion.forVersion("6.7.1")).isEqualTo(ElasticVersion.V6_7);
 
@@ -69,7 +66,6 @@
 
   @Test
   public void atLeastMinorVersion() throws Exception {
-    assertThat(ElasticVersion.V6_6.isAtLeastMinorVersion(ElasticVersion.V6_7)).isFalse();
     assertThat(ElasticVersion.V6_7.isAtLeastMinorVersion(ElasticVersion.V6_7)).isTrue();
     assertThat(ElasticVersion.V6_8.isAtLeastMinorVersion(ElasticVersion.V6_8)).isTrue();
     assertThat(ElasticVersion.V7_0.isAtLeastMinorVersion(ElasticVersion.V6_7)).isFalse();
@@ -85,7 +81,6 @@
 
   @Test
   public void version6OrLater() throws Exception {
-    assertThat(ElasticVersion.V6_6.isV6OrLater()).isTrue();
     assertThat(ElasticVersion.V6_7.isV6OrLater()).isTrue();
     assertThat(ElasticVersion.V6_8.isV6OrLater()).isTrue();
     assertThat(ElasticVersion.V7_0.isV6OrLater()).isTrue();
@@ -101,7 +96,6 @@
 
   @Test
   public void version7OrLater() throws Exception {
-    assertThat(ElasticVersion.V6_6.isV7OrLater()).isFalse();
     assertThat(ElasticVersion.V6_7.isV7OrLater()).isFalse();
     assertThat(ElasticVersion.V6_8.isV7OrLater()).isFalse();
     assertThat(ElasticVersion.V7_0.isV7OrLater()).isTrue();