docs: remove Enterprise Starter from Slack integration support (#1731)

Author: eseliger

docs/slack-integration.mdx

@@ -1,8 +1,7 @@
 # Slack Integration
 
 <TierCallout>
-	Supported on [Enterprise Starter](/pricing/plans/enterprise-starter) and
-	[Enterprise](/pricing/plans/enterprise) plans.
+	Supported on [Enterprise](/pricing/plans/enterprise) plans.
 </TierCallout>
 
 The Sourcegraph Slack integration brings the power of [Deep Search](/deep-search) directly into your Slack workspace. When you mention `@Sourcegraph` in any Slack channel or thread, a Deep Search conversation starts right there—no context switching required.