Remove compatibility testing with older Java versions (#112838)

We've bumped the minimum runtime Java version for Elasticsearch 9.0 to
Java 21 so we need to remove testing against older versions. I've also
removed redundant testing of the current bundled JDK version as well as
the old matrix config files that were used with Jenkins.

.buildkite/pipelines/periodic.template.yml

@@ -46,7 +46,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - openjdk17
+              - openjdk21
             GRADLE_TASK:
               - checkPart1
               - checkPart2
@@ -88,10 +88,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - graalvm-ce17
-              - openjdk17
               - openjdk21
-              - openjdk22
               - openjdk23
             GRADLE_TASK:
               - checkPart1
@@ -115,10 +112,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - graalvm-ce17
-              - openjdk17
               - openjdk21
-              - openjdk22
               - openjdk23
             BWC_VERSION: $BWC_LIST
         agents:

.buildkite/pipelines/periodic.yml

@@ -407,7 +407,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - openjdk17
+              - openjdk21
             GRADLE_TASK:
               - checkPart1
               - checkPart2
@@ -449,10 +449,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - graalvm-ce17
-              - openjdk17
               - openjdk21
-              - openjdk22
               - openjdk23
             GRADLE_TASK:
               - checkPart1
@@ -476,10 +473,7 @@ steps:
         matrix:
           setup:
             ES_RUNTIME_JAVA:
-              - graalvm-ce17
-              - openjdk17
               - openjdk21
-              - openjdk22
               - openjdk23
             BWC_VERSION: ["8.15.2", "8.16.0", "9.0.0"]
         agents: