chore: drop gradle-8 and oraclejdk-8 images

Remove the Gradle 8 and Oracle JDK 8 image directories, their publish
workflows, and the corresponding rows and sections in the root README.

README.md

@@ -7,8 +7,6 @@ Custom Docker images of legacy/discontinued software — built and published to
 | Image | Tag | GHCR package | Notes |
 |-------|-----|-------------|-------|
 | Couchbase 2.5 | `2.5.2` | [couchbase-2.5](https://github.com/tiennm99/docker-images/pkgs/container/couchbase-2.5) | Legacy NoSQL; no official image exists |
-| Gradle 8 | latest | — | JDK 8 + Corretto base |
-| Oracle JDK 8 | `8u201` | — | Archived Oracle JDK build |
 | Scribe 2.2 | `2.2` | [scribe](https://github.com/tiennm99/docker-images/pkgs/container/scribe) | Facebook's legacy log aggregation daemon |
 
 ## Couchbase-2.5
@@ -27,21 +25,6 @@ Docker Compose example: [couchbase-2.5/docker-compose.example.yml](couchbase-2.5
 - https://github.com/couchbase/docker/tree/14f9e5f37723ef15affa8cf3227b15409805f668/enterprise/couchbase-server/2.5.2
 - https://github.com/couchbase/docker/tree/a9e69006c4dae3d6b8aa4055436c83e9cd51d9e4/enterprise/couchbase-server/2.5.2
 
-## Gradle 8
-
-### Credits
-
-- https://gradle.org/releases/#8.13
-- https://github.com/gradle/docker-gradle/blob/8/jdk8-corretto/Dockerfile
-
-## Oracle JDK 8
-
-### Credits
-
-- https://www.oracle.com/java/technologies/javase/javase8-archive-downloads.html
-- https://github.com/oracle/docker-images/blob/main/OracleJava/8/jdk/Dockerfile.ol8
-- https://repo.huaweicloud.com/java/jdk/8u201-b09/
-
 ## Scribe 2.2
 
 Facebook's legacy real-time log aggregation daemon.