Remove channel export plugin from transitional plugins list. Channel export plugin is now prepackaged. (#30193)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/plugin.go

@@ -1074,7 +1074,6 @@ var transitionallyPrepackagedPlugins = []string{
 	"focalboard",
 	"mattermost-autolink",
 	"com.mattermost.aws-sns",
-	"com.mattermost.plugin-channel-export",
 	"com.mattermost.confluence",
 	"com.mattermost.custom-attributes",
 	"jenkins",