MM-31064: Simplify indentation (#16565)

* MM-31064: Simplify indentation

Reduce indentation where possible.

```release-note
NONE
```

Command ran to verify:
golangci-lint run --disable-all --enable golint --max-issues-per-linter=10000 --max-same-issues=100000 ./... | grep "block ends with a return state"

https://mattermost.atlassian.net/browse/MM-31064

* incorporate review comments

* enable golint for outdent rule

* fix remaining issues

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/slashcommands/command_invite.go

@@ -113,14 +113,13 @@ func (*InviteProvider) DoCommand(a *app.App, args *model.CommandArgs, message st
 					}),
 					ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL,
 				}
-			} else {
-				// User doing the inviting is *not* a member of the channel.
-				return &model.CommandResponse{
-					Text: args.T("api.command_invite.private_channel.app_error", map[string]interface{}{
-						"Channel": channelToJoin.Name,
-					}),
-					ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL,
-				}
+			}
+			// User doing the inviting is *not* a member of the channel.
+			return &model.CommandResponse{
+				Text: args.T("api.command_invite.private_channel.app_error", map[string]interface{}{
+					"Channel": channelToJoin.Name,
+				}),
+				ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL,
 			}
 		}
 	default: