Remove SHA pin from cockroachdb entry

Let installs follow the repo's default branch instead of a fixed SHA.
Removes the plugin from the weekly SHA-bump rotation and lets developer
updates reach users directly on `claude plugin install`.

.claude-plugin/marketplace.json

@@ -364,8 +364,7 @@
       "category": "database",
       "source": {
         "source": "url",
-        "url": "https://github.com/cockroachdb/claude-plugin.git",
-        "sha": "2263d09ec5dff0ba4042bb9074c3719d064d934a"
+        "url": "https://github.com/cockroachdb/claude-plugin.git"
       },
       "homepage": "https://github.com/cockroachdb/claude-plugin"
     },