feat: remove all legacy handlers (#795)

## Description

Closes: #566 

This PR removes all legacy handlers since it is no longer used.

See: cosmos/cosmos-sdk#7517



---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/desmos-labs/desmos/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://docs.cosmos.network/v0.44/building-modules/intro.html)
- [ ] included the necessary unit and integration [tests](https://github.com/desmos-labs/desmos/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

x/profiles/module.go

@@ -137,14 +137,9 @@ func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
 	keeper.RegisterInvariants(ir, am.keeper)
 }
 
-// Route returns the message routing key for the profiles module.
+// Deprecated: Route returns the module's message router and handler.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.keeper))
-}
-
-// NewHandler returns an sdk.Handler for the profiles module.
-func (am AppModule) NewHandler() sdk.Handler {
-	return NewHandler(am.keeper)
+	return sdk.Route{}
 }
 
 // QuerierRoute returns the profiles module's querier route name.

x/relationships/module.go

@@ -143,14 +143,9 @@ func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
 	keeper.RegisterInvariants(ir, am.keeper)
 }
 
-// Route returns the message routing key for the relationships module.
+// Deprecated: Route returns the module's message router and handler.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.keeper))
-}
-
-// NewHandler returns an sdk.Handler for the relationships module.
-func (am AppModule) NewHandler() sdk.Handler {
-	return NewHandler(am.keeper)
+	return sdk.Route{}
 }
 
 // QuerierRoute returns the relationships module's querier route name.

x/subspaces/module.go

@@ -124,14 +124,9 @@ func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
 	keeper.RegisterInvariants(ir, am.keeper)
 }
 
-// Route returns the message routing key for the subspaces module.
+// Deprecated: Route returns the module's message router and handler.
 func (am AppModule) Route() sdk.Route {
-	return sdk.NewRoute(types.RouterKey, NewHandler(am.keeper))
-}
-
-// NewHandler returns an sdk.Handler for the subspaces module.
-func (am AppModule) NewHandler() sdk.Handler {
-	return NewHandler(am.keeper)
+	return sdk.Route{}
 }
 
 // QuerierRoute returns the subspaces module's querier route name.