Remove support for vulnerable ES versions

Vulnerable ES versions older than v7.16 are removed[1] as they
don't have fix for the Log4J v2 vulnerability CVE-2021-44228[2].

Elasticsearch docker image for tests are unchanged. See the
justification in I951ce5e6.

[1] https://discuss.elastic.co/t/apache-log4j2-remote-code-execution-rce-vulnerability-cve-2021-44228-esa-2021-31/291476
[2] https://nvd.nist.gov/vuln/detail/CVE-2021-44228

Bug: Issue 15481
Change-Id: I5bfb8971efea1be787de52addec5cab37d38133f

src/main/java/com/google/gerrit/elasticsearch/ElasticVersion.java

diff --git a/src/main/java/com/google/gerrit/elasticsearch/ElasticVersion.java b/src/main/java/com/google/gerrit/elasticsearch/ElasticVersion.java
index baea46b..dffdf3e 100644
--- a/src/main/java/com/google/gerrit/elasticsearch/ElasticVersion.java
+++ b/src/main/java/com/google/gerrit/elasticsearch/ElasticVersion.java
@@ -18,10 +18,6 @@
 import java.util.regex.Pattern;
 
 public enum ElasticVersion {
-  V7_6("7.6.*"),
-  V7_7("7.7.*"),
-  V7_8("7.8.*"),
-  V7_10("7.10.*"),
   V7_16("7.16.*");
 
   private final String version;

src/test/java/com/google/gerrit/elasticsearch/ElasticContainer.java

diff --git a/src/test/java/com/google/gerrit/elasticsearch/ElasticContainer.java b/src/test/java/com/google/gerrit/elasticsearch/ElasticContainer.java
index 4567acf..4fddc72 100644
--- a/src/test/java/com/google/gerrit/elasticsearch/ElasticContainer.java
+++ b/src/test/java/com/google/gerrit/elasticsearch/ElasticContainer.java
@@ -41,14 +41,6 @@
 
   private static String getImageName(ElasticVersion version) {
     switch (version) {
-      case V7_6:
-        return "docker.elastic.co/elasticsearch/elasticsearch:7.6.2";
-      case V7_7:
-        return "docker.elastic.co/elasticsearch/elasticsearch:7.7.1";
-      case V7_8:
-        return "docker.elastic.co/elasticsearch/elasticsearch:7.8.1";
-      case V7_10:
-        return "docker.elastic.co/elasticsearch/elasticsearch:7.10.0";
       case V7_16:
         return "docker.elastic.co/elasticsearch/elasticsearch:7.16.2";
     }

src/test/java/com/google/gerrit/elasticsearch/ElasticVersionTest.java

diff --git a/src/test/java/com/google/gerrit/elasticsearch/ElasticVersionTest.java b/src/test/java/com/google/gerrit/elasticsearch/ElasticVersionTest.java
index 19b7e31..ea7782b 100644
--- a/src/test/java/com/google/gerrit/elasticsearch/ElasticVersionTest.java
+++ b/src/test/java/com/google/gerrit/elasticsearch/ElasticVersionTest.java
@@ -22,18 +22,6 @@
 public class ElasticVersionTest {
   @Test
   public void supportedVersion() throws Exception {
-    assertThat(ElasticVersion.forVersion("7.6.0")).isEqualTo(ElasticVersion.V7_6);
-    assertThat(ElasticVersion.forVersion("7.6.1")).isEqualTo(ElasticVersion.V7_6);
-
-    assertThat(ElasticVersion.forVersion("7.7.0")).isEqualTo(ElasticVersion.V7_7);
-    assertThat(ElasticVersion.forVersion("7.7.1")).isEqualTo(ElasticVersion.V7_7);
-
-    assertThat(ElasticVersion.forVersion("7.8.0")).isEqualTo(ElasticVersion.V7_8);
-    assertThat(ElasticVersion.forVersion("7.8.1")).isEqualTo(ElasticVersion.V7_8);
-
-    assertThat(ElasticVersion.forVersion("7.10.0")).isEqualTo(ElasticVersion.V7_10);
-    assertThat(ElasticVersion.forVersion("7.10.1")).isEqualTo(ElasticVersion.V7_10);
-
     assertThat(ElasticVersion.forVersion("7.16.0")).isEqualTo(ElasticVersion.V7_16);
     assertThat(ElasticVersion.forVersion("7.16.1")).isEqualTo(ElasticVersion.V7_16);
   }