chore: remove unnecessary legacy handler from qgb module (#2635)

<!--
Please read and fill out this form before submitting your PR.

Please make sure you have reviewed our contributors guide before
submitting your
first PR.
-->

## Overview

<!--
Please provide an explanation of the PR, including the appropriate
context,
background, goal, and rationale. If there is an issue with this
information,
please provide a tl;dr and link the issue.
-->

## Checklist

<!--
Please complete the checklist to ensure that the PR is ready to be
reviewed.

IMPORTANT:
PRs should be left in Draft until the below checklist is completed.
-->

- [ ] New and updated code has appropriate documentation
- [ ] New and updated code has new and/or updated testing
- [ ] Required CI checks are passing
- [ ] Visual proof for any user facing features like CLI or
documentation updates
- [ ] Linked issues closed with keywords

(cherry picked from commit 3914153)

x/qgb/module.go

@@ -114,7 +114,7 @@ func (am AppModule) Name() string {
 
 // Route returns the capability module's message routing key.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.keeper))
+	return sdk.Route{}
 }
 
 // QuerierRoute returns the capability module's query routing key.