fix: corrupt data in routes() response due to healthchecker data

[Revolyssup]

Description

Fixes # (issue)
Currently there is an intermittent bug. Below are the steps to reproduce:
Reproduction steps

1. Create a route and enable health check

curl http://127.0.0.1:9180/apisix/admin/routes/1 -H 'X-API-KEY: wqGBivhkYbFXiMdcMEAOMZanCGnLSbWE' -X PUT -d '
{
    "uri": "/*",
    "upstream": {
         "nodes": {
            "httpbin.org:80": 1,
            "mockbin.org:80": 1
        },
        "type": "roundrobin",
        "checks": {
            "active": {
                "timeout": 5,
                "type": "tcp",
                "healthy": {
                    "interval": 2,
                    "successes": 1
                },                
                "unhealthy": {
                    "interval": 2,
                    "successes": 1
                }
            }
        }
    }
}'

2. access routes to trigger health checks

curl http://127.0.0.1:9080/get

3. When accessing the control api, 500 will be returned and the error in the problem description will be generated.

Checklist

This error is intermittent and multiple tries might be needed to reproduce.
On debugging it was found that the cause of issue was http_router.user_routes table being polluted by adding healthchecks leaving unexpected data which while trying to parse, the error was generated.

As you can see in the generated logs, user_route returned healthchecker data.

Fix

Remove healthcheck related objects before sending to user.

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[membphis]

we can not update the watched data from etcd, it is dangerous

[Revolyssup]

we can not update the watched data from etcd, it is dangerous

The original data is not being modified. It is already deepcopied. But to make it easier to review I have refactored to move the modification logic just below the deepcopy function call so that it's clear that the original data is not being modified.

[nic-chen]

why not just also set to nil

[Revolyssup]

some existing test cases grep logs and expect this to {}

[nic-chen]

Then you can fix the test case as well.
Checking the logs has no meaning for the control api.