revert kaniko cache to reduce build memory pressure

Host is RAM-constrained (3.6G, no swap originally); builds were OOM-killing other containers. Mitigated at the host (swap + agent per-step mem limit); drop kaniko cache to keep build memory footprint minimal.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.woodpecker.yml

@@ -16,8 +16,6 @@ steps:
       tags: latest
       repo: woni/office-xbot-feishu
       registry: registry.woni.link
-      cache: true
-      cache_repo: woni/office-xbot-feishu-cache
       mirrors:
         - 5c492fmo.mirror.aliyuncs.com
       dockerfile: ./Dockerfile