[relay-compiler] Local persist does not delete old versions of query

I recently set up local persisted queries and noticed that subsequent updates seem to be additive vs replacing the existing queries in the persisted config

Example:
If i have a `TestQuery` which gets saved in the persisted config as
```
"12345": "query TestQuery..."
```

and i later make a change to `TestQuery` and rerun relay-compiler, my json file will look like:
```
"12345": "query TestQuery...", <-- this is the old version of my query
"23456": "query TestQuery..." <-- this is the new version of my query
```

The only way I've found to generate a "fresh" copy of the json file is to first delete the json file and then run relay compiler with the `--repersist` flag.

Wanted to validate if this is expected behavior or not (could not find anything in the docs or source code to confirm this).

Thanks in advance!