Revert "add register index.ts in slack"

This reverts commit 3c1a2c1f8bf155a46a6d85de5635a717789af078.

packages/slack/src/index.ts

@@ -5,5 +5,4 @@ export const supportedSlackCommands: string[] = [
 export const supportedGrowiCommands: string[] = [
   'search',
   'create',
-  'register',
 ];