Revert "Pre-install all TiDB versions in Docker image"

This reverts commit 53f9992.

Author: zph

Dockerfile.tiup-playground

@@ -1,6 +1,5 @@
 # Dockerfile for TiUP Playground container
 # This image contains TiUP and can run TiDB Playground inside a container
-# Pre-installs all TiDB versions used in tests to avoid downloads during test runs
 
 FROM ubuntu:22.04
 
@@ -22,31 +21,6 @@ ENV PATH="/root/.tiup/bin:${PATH}"
 RUN /root/.tiup/bin/tiup update --self && \
     /root/.tiup/bin/tiup update playground || true
 
-# Pre-install all TiDB versions used in tests
-# This avoids downloading components during test runs, making tests faster
-# Versions must match .github/workflows/main.yml env.TIDB_VERSIONS
-RUN /root/.tiup/bin/tiup install tidb:v6.1.7 && \
-    /root/.tiup/bin/tiup install tidb:v6.5.12 && \
-    /root/.tiup/bin/tiup install tidb:v7.1.6 && \
-    /root/.tiup/bin/tiup install tidb:v7.5.7 && \
-    /root/.tiup/bin/tiup install tidb:v8.1.2 && \
-    /root/.tiup/bin/tiup install tidb:v8.5.3 || true
-
-# Also pre-install PD and TiKV components for these versions (needed by playground)
-# Note: TiUP playground will download these if not present, but pre-installing speeds things up
-RUN /root/.tiup/bin/tiup install pd:v6.1.7 && \
-    /root/.tiup/bin/tiup install tikv:v6.1.7 && \
-    /root/.tiup/bin/tiup install pd:v6.5.12 && \
-    /root/.tiup/bin/tiup install tikv:v6.5.12 && \
-    /root/.tiup/bin/tiup install pd:v7.1.6 && \
-    /root/.tiup/bin/tiup install tikv:v7.1.6 && \
-    /root/.tiup/bin/tiup install pd:v7.5.7 && \
-    /root/.tiup/bin/tiup install tikv:v7.5.7 && \
-    /root/.tiup/bin/tiup install pd:v8.1.2 && \
-    /root/.tiup/bin/tiup install tikv:v8.1.2 && \
-    /root/.tiup/bin/tiup install pd:v8.5.3 && \
-    /root/.tiup/bin/tiup install tikv:v8.5.3 || true
-
 # Default command runs TiUP Playground
 # This will be overridden by testcontainers with specific version and port
 CMD ["/root/.tiup/bin/tiup", "playground"]